December 29, 2015
December 23, 2015
Polymers
Polymers
General introduction and classification of polymers, general methods of polymerization - addition and condensation, copolymerization;
Natural and synthetic rubber and vulcanization; some important polymers with emphasis on their monomers and uses - polythene, nylon, polyester and bakelite.
Important Terms
Coordination compounds: coordination compounds are a special class of compounds in which the central atom is surrounded by ions and atoms beyond their normal valency
OR
Coordination or complex compounds may be defined as a molecular compound that results from the combination of two or more simple stable molecular compounds and retains its identity in the solid as well as in the dissolved state .The properties of such compounds are totally different than individual constituents. A coordination compound contains very often but not always a complex ion.
Complex ion
An electrically charged species which consists of a central metal ion or atom surrounded by a group of ions or neutral molecules(it may be noted that a complex may be positively charged or negatively charged or neutral).
Types of complex:
1.cationic complex
2.anionic complex
3.neutral complex
cationic complex :A complex which has net positive charge .
anionic complex : A complex which has net negative charge .
neutral complex: A complex which has no net charge or simply neutral.
TERMINOLOGY OF COORDINATION COMPOUNDS:
1 .Ligands:
The neutral molecule or ions which are directly attached to the central metal ion or atom through coordinate bonds in the complex ion is called Ligand.
>Ligands should have lone pair of electrons
>Ligands donate the lone pair to the central metal atom or ion forming coordinate covalent bond .
>thus Ligand are Lewis bases and central metal ion is a Lewis acid.
Types of ligands:
1. monodentate or unidentate ligands :ligand having only one donor atom.
2.bidentate ligand :ligand having two donor atoms
3.polydentate ligand :ligand having more than two donor atoms.
(tridentate,tetradentate,pentadentate,hexadentate,etc)
Chelating ligands:
when a bidentate or a polydentate ligand is attached by two or more donor atoms to the same central metal ion or atom forming a ring structure ,the ligand is called a chelating ligand. Chelating ligand forms a ring structure around the central metal ion.
Ambident ligand:
The monodentate ligands which can coordinate with the central metal ion or atom through more than one site are called ambident ligand.e.g.CN
M CN (cyanide)
M NC(isocyanide)
2.Coordination number:
The total number of ligands attached to the central metal ion or atom is called the coordination number of the metal atom or ion.
3.Coordination sphere:
The central metal ion or atom and the ligands are collectively called the coordination sphere .
(in other words the ions present in the square bracket together are called the coordination sphere)
4. Charge of a complex:
the charge carried by a complex ion is the algebraic sum of the charges carried by the central ion and the ligands coordinated to it .
OR
Coordination or complex compounds may be defined as a molecular compound that results from the combination of two or more simple stable molecular compounds and retains its identity in the solid as well as in the dissolved state .The properties of such compounds are totally different than individual constituents. A coordination compound contains very often but not always a complex ion.
Complex ion
An electrically charged species which consists of a central metal ion or atom surrounded by a group of ions or neutral molecules(it may be noted that a complex may be positively charged or negatively charged or neutral).
Types of complex:
1.cationic complex
2.anionic complex
3.neutral complex
cationic complex :A complex which has net positive charge .
anionic complex : A complex which has net negative charge .
neutral complex: A complex which has no net charge or simply neutral.
TERMINOLOGY OF COORDINATION COMPOUNDS:
1 .Ligands:
The neutral molecule or ions which are directly attached to the central metal ion or atom through coordinate bonds in the complex ion is called Ligand.
>Ligands should have lone pair of electrons
>Ligands donate the lone pair to the central metal atom or ion forming coordinate covalent bond .
>thus Ligand are Lewis bases and central metal ion is a Lewis acid.
Types of ligands:
1. monodentate or unidentate ligands :ligand having only one donor atom.
2.bidentate ligand :ligand having two donor atoms
3.polydentate ligand :ligand having more than two donor atoms.
(tridentate,tetradentate,pentadentate,hexadentate,etc)
Chelating ligands:
when a bidentate or a polydentate ligand is attached by two or more donor atoms to the same central metal ion or atom forming a ring structure ,the ligand is called a chelating ligand. Chelating ligand forms a ring structure around the central metal ion.
Ambident ligand:
The monodentate ligands which can coordinate with the central metal ion or atom through more than one site are called ambident ligand.e.g.CN
M CN (cyanide)
M NC(isocyanide)
2.Coordination number:
The total number of ligands attached to the central metal ion or atom is called the coordination number of the metal atom or ion.
3.Coordination sphere:
The central metal ion or atom and the ligands are collectively called the coordination sphere .
(in other words the ions present in the square bracket together are called the coordination sphere)
4. Charge of a complex:
the charge carried by a complex ion is the algebraic sum of the charges carried by the central ion and the ligands coordinated to it .
haloform reaction
When methyl ketones are treated with the halogen in basic solution, polyhalogenaton followed by cleavage of the methyl group occurs.
The products are the carboxylate and trihalomethane, otherwise known as haloform.
The reaction proceeds via successively faster halogenations at the α-position until the 3 H have been replaced.
The halogenations get faster since the halogen stablises the enolate negative charge and makes it easier to form.
Then a nucleophilic acyl substitution by hydroxide displaces the anion CX3(haloform) as a leaving group that rapidly protonates.
This reaction is often performed using iodine and as a chemical test for identifying methyl ketones. Iodoform(CI3) is yellow and precipitates under the reaction conditions.
Reaction mechanism
Step 1:
First, an acid-base reaction. Hydroxide functions as a base and removes the acidic α-hydrogen giving the enolate.
Step 2:
The nucleophilic enolate reacts with the iodine giving the halogenated ketone and an iodide ion.
Step 3:
Steps 1 and 2 repeat twice more yielding the trihalogenated ketone.
Step 4:
The hydroxide now reacts as a nucleophile at the electrophilic carbonyl carbon, with the C=O becoming a C-O single bond and the oxygen is now anionic.
Step 5:
Reform the favourable C=O and displace a leaving group, the trihalomethyl system which is stabilised by the 3 halogens. This gives the carboxylic acid.
Step 6:
An acid-base reaction. The trihalomethyl anion is protonated by the carboxylic acid, giving the carboxylate and the haloform (trihalomethane).
The products are the carboxylate and trihalomethane, otherwise known as haloform.
The reaction proceeds via successively faster halogenations at the α-position until the 3 H have been replaced.
The halogenations get faster since the halogen stablises the enolate negative charge and makes it easier to form.
Then a nucleophilic acyl substitution by hydroxide displaces the anion CX3(haloform) as a leaving group that rapidly protonates.
This reaction is often performed using iodine and as a chemical test for identifying methyl ketones. Iodoform(CI3) is yellow and precipitates under the reaction conditions.
Reaction mechanism
Step 1:
First, an acid-base reaction. Hydroxide functions as a base and removes the acidic α-hydrogen giving the enolate.
Step 2:
The nucleophilic enolate reacts with the iodine giving the halogenated ketone and an iodide ion.
Step 3:
Steps 1 and 2 repeat twice more yielding the trihalogenated ketone.
Step 4:
The hydroxide now reacts as a nucleophile at the electrophilic carbonyl carbon, with the C=O becoming a C-O single bond and the oxygen is now anionic.
Step 5:
Reform the favourable C=O and displace a leaving group, the trihalomethyl system which is stabilised by the 3 halogens. This gives the carboxylic acid.
Step 6:
An acid-base reaction. The trihalomethyl anion is protonated by the carboxylic acid, giving the carboxylate and the haloform (trihalomethane).
aldol condensation
Aldehydes and ketones containing α-hydrogen (H-atoms attached to the C-atom adjacent to the carbonyl group)undergo condensation in the presence of dilute alkali.
In the resulting compound both aldehyde group and alcohol group are present.
acetaldehyde and acetone undergo aldol condensation.
Formaldehyde, banzaldehyde do not undergo aldol condensation.
Reagents : commonly a base such as NaOH or KOH is added to the aldehyde.
The reaction involves an enolate reacting with another molecule of the aldehyde.
Remember enolates are good nucleophiles and carbonyl C are electrophiles.
Since the pKa of an aldehyde is close to that of NaOH, both enolate and aldehyde are present.
The products of these reactions are β-hydroxyaldehydes or aldehyde-alcohols = aldols.
The simplest aldol reaction is the condensation of ethanal.
Step 1:
First, an acid-base reaction. Hydroxide functions as a base and removes the acidic α-hydrogen giving the reactive enolate.
Step 2:
The nucleophilic enolate attacks the aldehyde at the electrophilic carbonyl C in a nucleophilic addition type process giving an intermediate alkoxide.
Step 3:
An acid-base reaction. The alkoxide deprotonates a water molecule creating hydroxide and the β-hydroxyaldehydes or aldol product.
In the resulting compound both aldehyde group and alcohol group are present.
acetaldehyde and acetone undergo aldol condensation.
Formaldehyde, banzaldehyde do not undergo aldol condensation.
Reagents : commonly a base such as NaOH or KOH is added to the aldehyde.
The reaction involves an enolate reacting with another molecule of the aldehyde.
Remember enolates are good nucleophiles and carbonyl C are electrophiles.
Since the pKa of an aldehyde is close to that of NaOH, both enolate and aldehyde are present.
The products of these reactions are β-hydroxyaldehydes or aldehyde-alcohols = aldols.
The simplest aldol reaction is the condensation of ethanal.
Step 1:
First, an acid-base reaction. Hydroxide functions as a base and removes the acidic α-hydrogen giving the reactive enolate.
Step 2:
The nucleophilic enolate attacks the aldehyde at the electrophilic carbonyl C in a nucleophilic addition type process giving an intermediate alkoxide.
Step 3:
An acid-base reaction. The alkoxide deprotonates a water molecule creating hydroxide and the β-hydroxyaldehydes or aldol product.
Cannizzaro reaction
Aldehydes which do not have α-hydrogen atom react with concentrated sodium hydroxide (NaOH) or potassium hydroxide (KOH) in such a way that one molecule get oxidized to acid and the second molecule gets reduced to alcohol.
Note two molecules of aldehyde participates in the reaction.
This self oxidation-reduction under the influence of a base is known as the Cannizzaro's reaction.
Formaldehyde does not possess α-hydrogen atom and therefore undergoes Cannizzaro's reaction. Acetaldehyde does not give this reaction.
Formaldehyde (HCHO) two molecules + warm NaOH give Methanol (CH3OH) and Sodium Formate (CHOONa)
CH3OH is the reduction product HCHO becomes CH3OH (two hydrogen atoms are getting in).
CHOONa is the oxidation product. one 'H' has gone out and One 'O' came in along with Na.
Note two molecules of aldehyde participates in the reaction.
This self oxidation-reduction under the influence of a base is known as the Cannizzaro's reaction.
Formaldehyde does not possess α-hydrogen atom and therefore undergoes Cannizzaro's reaction. Acetaldehyde does not give this reaction.
Formaldehyde (HCHO) two molecules + warm NaOH give Methanol (CH3OH) and Sodium Formate (CHOONa)
CH3OH is the reduction product HCHO becomes CH3OH (two hydrogen atoms are getting in).
CHOONa is the oxidation product. one 'H' has gone out and One 'O' came in along with Na.
Aldehydes and Ketones - Chemical Properties
Reactions
Can studied with the following grouping
A. Nucleophilic addition reactions.
B. Nucleophilic addition reactions that involve elimination of water molecule
C. Oxidation reactions
D. Reduction reactions
E. Miscellaneous reactions
A. Nucleophilic addition reactions
1. Hydrogen cyanide: addition product is cyanohydrin
2. Sodium bisulphite: addition proudct is bisulphite adduct.
3. Grignard reagent: addition intermediate product, when hydrolysed gives alcohol
4. Alcohol: product geminal dialkoxy compounds.
B. Nucleophilic addition reactions that involve elimination of water molecule
Aldehydes and ketones react with a number of ammonia derivatives in weakly acidic medium to form compound containing carbon-nitrogen double bonds with the elimination of water molecule.
1. Addition of various ammonia derivatives
i) Hydroxylamine - product oxime[The condensation of aldehydes with hydroxylamine gives aldoxime. Ketoximes are produced from ketones and hydroxylamine.Generally, oximes exist as colorless crystals and do not easily dissolve in water. Oximes can be used for the identification of ketone or aldehyde.]
ii) Hydrazine - product hydrazone
iii) Phenylhydrazine - product phenylhydrazone
iv) 2, 4 dinitrophenyl hydrazine - product 2,4 dinitrophenyl hydrazone
v) Semicarbazide - product semicarbazone
2. Addition of Ammonia
product aldehyde-ammonia ducts
3. Primary amines
product azomethines also known as Schiff bases.
C. Oxidation reactions
i) Tollen's reagent - silver mirror test
[Oxidation of Aldehydes by Silver Oxide: Reaction of simple aldehydes with aqueous Ag2O in the presence of NH3 yields the corresponding carboxylic acid and metallic silver. The silver is generally deposited in a thin metallic layer which forms a reflective "mirror" on the inside surface of the reaction vessel. The formation of this mirror forms the basis of a qualitative test for aldehydes, called the Tollens Test. ]
ii) Fehling's solution - aldehydes give a red precipitate of cuprous oxide
iii) Benedict's solutin - similar to Fehling's solution
iv) Oxidation with sodium hypohalite - iodoform is the product
D. Reduction of aldehydes and ketones
1. Reduction to alcohols: aldehydes give primary alcohols. Ketones give secondary alcohols.
2. Reduction to hydrocarbons:
i) Reduction with zinc amalgam and con HCL
ii) Reductin with basic solution of hydrazine
iii) Reductioin with HI in the presence of red phosphorus
3. Reduction to pinacols
E. Miscellaneous reactions
1. Aldol condensation
2. Cross aldol condensation
3. Cannizaro's reaction
4. Halogenation
5. Action with Schiff's reagent
6. Polymerisation
7. Sunstitution reactions of benzene nucleus in aldehydes and ketones.
Can studied with the following grouping
A. Nucleophilic addition reactions.
B. Nucleophilic addition reactions that involve elimination of water molecule
C. Oxidation reactions
D. Reduction reactions
E. Miscellaneous reactions
A. Nucleophilic addition reactions
1. Hydrogen cyanide: addition product is cyanohydrin
2. Sodium bisulphite: addition proudct is bisulphite adduct.
3. Grignard reagent: addition intermediate product, when hydrolysed gives alcohol
4. Alcohol: product geminal dialkoxy compounds.
B. Nucleophilic addition reactions that involve elimination of water molecule
Aldehydes and ketones react with a number of ammonia derivatives in weakly acidic medium to form compound containing carbon-nitrogen double bonds with the elimination of water molecule.
1. Addition of various ammonia derivatives
i) Hydroxylamine - product oxime[The condensation of aldehydes with hydroxylamine gives aldoxime. Ketoximes are produced from ketones and hydroxylamine.Generally, oximes exist as colorless crystals and do not easily dissolve in water. Oximes can be used for the identification of ketone or aldehyde.]
ii) Hydrazine - product hydrazone
iii) Phenylhydrazine - product phenylhydrazone
iv) 2, 4 dinitrophenyl hydrazine - product 2,4 dinitrophenyl hydrazone
v) Semicarbazide - product semicarbazone
2. Addition of Ammonia
product aldehyde-ammonia ducts
3. Primary amines
product azomethines also known as Schiff bases.
C. Oxidation reactions
- Carbonyl groups in aldehydes and ketones may be oxidized to form compounds at the next “oxidation level”, that of carboxylic acids.
- Alcohols are oxidized to aldehydes and ketones (example: biological oxidation of ethanol to acetaldehyde)
- The carbonyl group may be further oxidized to carboxylic acids
- Oxidation of Aldehydes to form Carboxylic Acids: Reaction of simple aldehydes with acidic MnO4-, or CrO3/H2SO4 yields the corresponding carboxylic acid. Aldehydes oxidize very easily and it is often difficult to prevent oxidation, even by atmospheric oxygen.
Oxidation of Ketones: Ketones are more resistant to oxidation, but can be cleaved with acidic MnO4- to yield carboxylic acids.
i) Tollen's reagent - silver mirror test
[Oxidation of Aldehydes by Silver Oxide: Reaction of simple aldehydes with aqueous Ag2O in the presence of NH3 yields the corresponding carboxylic acid and metallic silver. The silver is generally deposited in a thin metallic layer which forms a reflective "mirror" on the inside surface of the reaction vessel. The formation of this mirror forms the basis of a qualitative test for aldehydes, called the Tollens Test. ]
ii) Fehling's solution - aldehydes give a red precipitate of cuprous oxide
iii) Benedict's solutin - similar to Fehling's solution
iv) Oxidation with sodium hypohalite - iodoform is the product
D. Reduction of aldehydes and ketones
1. Reduction to alcohols: aldehydes give primary alcohols. Ketones give secondary alcohols.
2. Reduction to hydrocarbons:
i) Reduction with zinc amalgam and con HCL
ii) Reductin with basic solution of hydrazine
iii) Reductioin with HI in the presence of red phosphorus
3. Reduction to pinacols
E. Miscellaneous reactions
1. Aldol condensation
2. Cross aldol condensation
3. Cannizaro's reaction
4. Halogenation
5. Action with Schiff's reagent
6. Polymerisation
7. Sunstitution reactions of benzene nucleus in aldehydes and ketones.
Aldehydes and Ketones - Methods of Preparation
1. From alkenes
2. From alkynes
3 From alcohols
4. From alkyl halides
5. From Grignard reagent
6. From carboxylic acids
7.From Acid chlorides
8.From alkyl cyanides
1. From alkenes
Alkenes react with ozone to form ozonide which on subsequent cleavage with zinc dust and water gives aldehydes and ketones.
2. From alkynes
Hydration of alkynes in the presence of dilute sulphuric acid and HgSO4 as catalyst gives aldehydes and ketones.
Water adds to alkynes to form unstable enol intermediates which rearrange to form aldehydes or ketones.
Hydration of acetylene gives acetaldehyde.
Hydration of alkynes other than acetylene gives ketones.
3. By oxidation of alcohols:
a) Primary alcohols on oxidation by potassium dichromate and dilute sulphuric acid give corresponding aldehyde
Potassium dichromate and sulphuric combine to give (0) nascent oxygen. Nascent oxygen oxidizes CH3OH to HCHO by removing H2 from CH3OH.
Nascent oxygen removes H2 from C2H5OH to give CH3CHO.
b)Ketones: Secondary alcohols on oxidation by potassium dichromate and dilute sulphuric acid mixture give ketones.
Isopropyl alcohol gives acetone.
2-butanol gives ethyl methyl ketone on oxidation.
2. From alkynes
3 From alcohols
4. From alkyl halides
5. From Grignard reagent
6. From carboxylic acids
7.From Acid chlorides
8.From alkyl cyanides
1. From alkenes
Alkenes react with ozone to form ozonide which on subsequent cleavage with zinc dust and water gives aldehydes and ketones.
2. From alkynes
Hydration of alkynes in the presence of dilute sulphuric acid and HgSO4 as catalyst gives aldehydes and ketones.
Water adds to alkynes to form unstable enol intermediates which rearrange to form aldehydes or ketones.
Hydration of acetylene gives acetaldehyde.
Hydration of alkynes other than acetylene gives ketones.
3. By oxidation of alcohols:
a) Primary alcohols on oxidation by potassium dichromate and dilute sulphuric acid give corresponding aldehyde
Potassium dichromate and sulphuric combine to give (0) nascent oxygen. Nascent oxygen oxidizes CH3OH to HCHO by removing H2 from CH3OH.
Nascent oxygen removes H2 from C2H5OH to give CH3CHO.
b)Ketones: Secondary alcohols on oxidation by potassium dichromate and dilute sulphuric acid mixture give ketones.
Isopropyl alcohol gives acetone.
2-butanol gives ethyl methyl ketone on oxidation.
Aldehydes ,Ketones Introduction and Nomenclature
Aldehydes contain carbonyl group C=O as functional group and the carbonyl atom carries at least one H atom.
Ketones
In ketones, also carbonyl group C=O is the functional group. But the carbonyl carbon does not contain any H atoms, but it is attached to two alkyl or aryl groups.
Getting an aldehyde from methylbenzene - by oxidation
Getting ketone from alcohols - By oxidation of secondary alcohols
Aldehydes and ketones are polar molecules because the C=O bond has a
dipole moment:
• Their polarity makes aldehydes and ketones have higher boiling points than
alkenes of similar molecular weight.
Aldehydes and Ketones – Nomenclature
Nomenclature of Aliphatic Aldehydes
Common system
Aldehydes are named according to the name of the corresponding acid which they form on oxidation.
The suffix –ic acid of the name of the acid is replaced by aldehyde.
Ex: The aldehyde that gives acetic acid is termed as acetaldehyde.
Braching in the aldehyde chain, is indicated by carbon atom positions α, β, γ, δ.
The carbon atom next to the carbonyl carbon is assigned the letter α. The carbon next to α-carbon is the β-carbon. The carbon next to β-carbon is the γ-carbon. The carbon next to γ-carbon is the δ Carbon.
δ - γ- β- α carbons
C-C-C-C-CHO
Ex: α-Methyl butyraldehyde
IUPAC system
Aldehydes are termed alkanals. The terminal ‘e’ of the name of corresponding alkane is replaced by ‘al’.
Ex: methanal, ethanal, propanal.
Nomenclature for Aldehydes with Branches
1. The longest chain containing –CHO group is considered as the parent chain and the name is derived as an alkanal.
2. To determine the number of the carbon where a substituent is attached to the aldehyde chain, the carbons in the chain are numbered in such a way that the aldehydic group carbon gets lowest number (i.e 1). In other words number of the aldehydic chain carbons is started from the carbon in the carbonyl group.
Nomenclature of Aromatic Aldehydes
The simplest aromatic aldehyde is benzaldehyde. In aromatic aldehydes, -CHO group is directly attached to the benzene ring.
In case of substituted aromatic aldehydes, the positions of the substituents in benzene ring with respect to –CHO group are indicated either by suffixes ortho, meta or para or by numbers 1,2,3… etc. with the carbon bearing the –CHO group as number 1.
Ex; 2-Hydroxybenaldehyde – OH is the substituent at the 2 carbon from CHO group.
The aldehydic group (CHO) can be a part of the side chain. In other words, an aldehydic group may be attached to benzene ring.
The name will be as an example 2-Phenylethanal. In this compound CH2CHO is attached to a benzene ring. The substituent is ethanal group, and the numbering of carbon atoms still starts from CHO group carbon and the terminology indicates that a benzyl group is attached to ethanal at 2nd carbon.
Nomenclature of Ketones
Common system
Ketones are named by using the names of alkyl groups present in the molecule.
Ex: Dimethyl ketone, Methyl isopropyl ketone
IUPAC system
Ketones are termed as alkanones.
Rules for arriving at names
1. The longest chain carrying the carbonyl groupis considered as the parent chain and the name is derived by replacing the terminal ‘e’ of the name of the corresponding alkane by letters ‘one’.
Ex: Propanone
2. In case of substituted ketones, theparent chain is numbered in such a way that the ketone group carbon gets the lowest number (but the numbering does not start from ketone group carbon – caron attached with a double bond to oxygen).
3. The position of carbonyl group and the substituents is indicated by numbers.
Ex: 3-methylbutan-2-one (indicated that there is methyl group at 3rd carbon and carbonyl group at 2nd carbon on butanone.
Compounds having both aldehyde and ketone groups.
For compounds having both aldehyde and ketone groups, the aldehyde group is considered as the principal functional group and ketonic group is regarded as substituent. It is named as prefix oxo- along with a number to indicate its position.
Ex: 2-Methyl-4-oxohexanal
Aromatic Ketones
Purely aromatic or mixed aromatics ketones are know by their common names.
Examples
Acetophenone – Methyl phenyl ketone
Propiophenone – Ethyl phenyl ketone
Benzophenone - Diphenyle ketone
IUPAC 1993 recommendation for 3 same functional groups
If an unbranched chain is directly bonded to more than two same functional groups, the organic compound is named as a derivative of parent alkane which does not include the carbon atoms of the functional groups. These compounds are named by use of suffix tricarboaldehyde (for three –CHO groups).
Ex: Butane-1,2,4-tricarbaldehyde
If three groups are not directly bonded to the unbranched carbon chain, the two like groups are considered in the parent chain and are named by using di before the name of the functional group. The third group forming the side chain is considered as a substituent group.
Ex: 3-Formylmethylhexane-1,6-dial (three –CHO groups are there. But at 1 and 6 they are directly bonded. At three there is a branching of the alkane chain and –CHO is attached to the methyl group of the branch).
Ketones
In ketones, also carbonyl group C=O is the functional group. But the carbonyl carbon does not contain any H atoms, but it is attached to two alkyl or aryl groups.
Getting an aldehyde from methylbenzene - by oxidation
Getting ketone from alcohols - By oxidation of secondary alcohols
Aldehydes and ketones are polar molecules because the C=O bond has a
dipole moment:
• Their polarity makes aldehydes and ketones have higher boiling points than
alkenes of similar molecular weight.
Aldehydes and Ketones – Nomenclature
Nomenclature of Aliphatic Aldehydes
Common system
Aldehydes are named according to the name of the corresponding acid which they form on oxidation.
The suffix –ic acid of the name of the acid is replaced by aldehyde.
Ex: The aldehyde that gives acetic acid is termed as acetaldehyde.
Braching in the aldehyde chain, is indicated by carbon atom positions α, β, γ, δ.
The carbon atom next to the carbonyl carbon is assigned the letter α. The carbon next to α-carbon is the β-carbon. The carbon next to β-carbon is the γ-carbon. The carbon next to γ-carbon is the δ Carbon.
δ - γ- β- α carbons
C-C-C-C-CHO
Ex: α-Methyl butyraldehyde
IUPAC system
Aldehydes are termed alkanals. The terminal ‘e’ of the name of corresponding alkane is replaced by ‘al’.
Ex: methanal, ethanal, propanal.
Nomenclature for Aldehydes with Branches
1. The longest chain containing –CHO group is considered as the parent chain and the name is derived as an alkanal.
2. To determine the number of the carbon where a substituent is attached to the aldehyde chain, the carbons in the chain are numbered in such a way that the aldehydic group carbon gets lowest number (i.e 1). In other words number of the aldehydic chain carbons is started from the carbon in the carbonyl group.
Nomenclature of Aromatic Aldehydes
The simplest aromatic aldehyde is benzaldehyde. In aromatic aldehydes, -CHO group is directly attached to the benzene ring.
In case of substituted aromatic aldehydes, the positions of the substituents in benzene ring with respect to –CHO group are indicated either by suffixes ortho, meta or para or by numbers 1,2,3… etc. with the carbon bearing the –CHO group as number 1.
Ex; 2-Hydroxybenaldehyde – OH is the substituent at the 2 carbon from CHO group.
The aldehydic group (CHO) can be a part of the side chain. In other words, an aldehydic group may be attached to benzene ring.
The name will be as an example 2-Phenylethanal. In this compound CH2CHO is attached to a benzene ring. The substituent is ethanal group, and the numbering of carbon atoms still starts from CHO group carbon and the terminology indicates that a benzyl group is attached to ethanal at 2nd carbon.
Nomenclature of Ketones
Common system
Ketones are named by using the names of alkyl groups present in the molecule.
Ex: Dimethyl ketone, Methyl isopropyl ketone
IUPAC system
Ketones are termed as alkanones.
Rules for arriving at names
1. The longest chain carrying the carbonyl groupis considered as the parent chain and the name is derived by replacing the terminal ‘e’ of the name of the corresponding alkane by letters ‘one’.
Ex: Propanone
2. In case of substituted ketones, theparent chain is numbered in such a way that the ketone group carbon gets the lowest number (but the numbering does not start from ketone group carbon – caron attached with a double bond to oxygen).
3. The position of carbonyl group and the substituents is indicated by numbers.
Ex: 3-methylbutan-2-one (indicated that there is methyl group at 3rd carbon and carbonyl group at 2nd carbon on butanone.
Compounds having both aldehyde and ketone groups.
For compounds having both aldehyde and ketone groups, the aldehyde group is considered as the principal functional group and ketonic group is regarded as substituent. It is named as prefix oxo- along with a number to indicate its position.
Ex: 2-Methyl-4-oxohexanal
Aromatic Ketones
Purely aromatic or mixed aromatics ketones are know by their common names.
Examples
Acetophenone – Methyl phenyl ketone
Propiophenone – Ethyl phenyl ketone
Benzophenone - Diphenyle ketone
IUPAC 1993 recommendation for 3 same functional groups
If an unbranched chain is directly bonded to more than two same functional groups, the organic compound is named as a derivative of parent alkane which does not include the carbon atoms of the functional groups. These compounds are named by use of suffix tricarboaldehyde (for three –CHO groups).
Ex: Butane-1,2,4-tricarbaldehyde
If three groups are not directly bonded to the unbranched carbon chain, the two like groups are considered in the parent chain and are named by using di before the name of the functional group. The third group forming the side chain is considered as a substituent group.
Ex: 3-Formylmethylhexane-1,6-dial (three –CHO groups are there. But at 1 and 6 they are directly bonded. At three there is a branching of the alkane chain and –CHO is attached to the methyl group of the branch).
Aldehyde , Ketones and Carboxylic Acids
Nomenclature, Isomerism, General methods of preparation, Physical properties,Chemical Properties Structure and Nature of (aldehydes and ketones)carbonyl group; Nucleophilic addition to >C=O group, relative reactivities of aldehydes and ketones; Important reactions such as - Nucleophilic addition reactions (addition of HCN, NH3 and its derivatives), Grignard reagent; oxidation; reduction (Wolff Kishner and Clemmensen); acidity of ? - hydrogen, aldol condensation, Cannizzaro reaction, Haloform reaction; Chemical tests to distinguish between aldehydes and Ketones.
Carboxylic Acids: Nomenclature, Isomerism, General methods of preparation, Physical properties, Chemical properties.Acidic strength and factors affecting it.
Further reading
Alcohols - Chemical Reactions
On the basis of structure of alcohols, their reactions may be divided into following types or groups for the purposes of study.
1. Reactions involving cleavage of oxygen-hydrogen bond.
2. Reactions involving cleavage of carbon-oxygen bond.
3. Reactions involving both the alkyl and hydroxyl groups.
1. Reactions involving cleavage of oxygen-hydrogen bond.
i) reaction with active metals
ii) reaction with metal hydrides
iii) reaction with carboxylic acids (esterification)
iv) reaction with Grignard reagents
v) Reaction with acyl chloride or acid anhydride (acylation)
2. Reactions involving cleavage of carbon-oxygen bond.
i) reaction with hydrogen haldies
ii) reaction with phosphorus halides
iii) reaction with thionyl chloride
3. Reactions involving both the alkyl and hydroxyl groups.
i) dehydration
ii) oxidation,
iii) dehydrogenation
reaction with ZnCl2/conc.-HCl, (Lucas test)
conversion of alcohols into aldehydes and ketones;
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1. Reactions involving cleavage of oxygen-hydrogen bond.
2. Reactions involving cleavage of carbon-oxygen bond.
3. Reactions involving both the alkyl and hydroxyl groups.
1. Reactions involving cleavage of oxygen-hydrogen bond.
i) reaction with active metals
ii) reaction with metal hydrides
iii) reaction with carboxylic acids (esterification)
iv) reaction with Grignard reagents
v) Reaction with acyl chloride or acid anhydride (acylation)
2. Reactions involving cleavage of carbon-oxygen bond.
i) reaction with hydrogen haldies
ii) reaction with phosphorus halides
iii) reaction with thionyl chloride
3. Reactions involving both the alkyl and hydroxyl groups.
i) dehydration
ii) oxidation,
iii) dehydrogenation
reaction with ZnCl2/conc.-HCl, (Lucas test)
conversion of alcohols into aldehydes and ketones;
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Alcohols -Reaction with active metals - acidic character
Alcohols are weakly acidic in nature.
They react with active metals such as sodium, potassium, magnesium, aluminium, etc. to liberate hydrogen gas and form metal alkoxide.
Liberation of hydrogen shows that alcohols are acidic in nature.
The acidic nature of alcohols is due to the presence of polar O-H bond.
As oxygen withdraws shared electron pair between O and H atoms towards itself, it can lose the proton (H+).
However, alcohols are weak acids
They react with active metals such as sodium, potassium, magnesium, aluminium, etc. to liberate hydrogen gas and form metal alkoxide.
Liberation of hydrogen shows that alcohols are acidic in nature.
The acidic nature of alcohols is due to the presence of polar O-H bond.
As oxygen withdraws shared electron pair between O and H atoms towards itself, it can lose the proton (H+).
However, alcohols are weak acids
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Esterification
Alcohols react with monocarboxylic acids, in the presence of concentrated sulphuric acid or dry HCL gas as catalyst, to from esters. This reaction is known as esterification.
Alcohols react with monocarboxylic acids, in the presence of concentrated sulphuric acid or dry HCL gas as catalyst, to from esters. This reaction is known as esterification.
The function of concentrated sulphuric acid is to act as protonating agent as well as a dehydrating agent.
RCOOH + HOR' ↔ RCOOR' + H2O with H2SO4 as catalyst
CH3COOH + HOC2H5 ↔ CH3COOC2H5 + H2O with H2SO4 as catalyst
The reaction is reversible is nature. Double headed arrow is used to indicate it. The equilibrium can be shifted toward the forward direction by removing water as soon as it is formed.
If dry HCL gas is used as a catalyst, the reaction is called Fisher=Speier esterification.
It is is difficult to prepare esters of tertiary alcohols becasue bulky groups in the alcohol decrease rate of reaction or esterification. This is termed as stearic hindrance of bulky groups.
As noted above in the reactions, esterification involved the cleavage of the O-H bonds of the alcohol. This was proved by using alcohol with isotopic O18 which can be tracked using isotopic tracer technique. It was found that this oxygen is present in the resulting ester which means that the oxygen in the alcohol is going into the ester and hydrogen is going into the water molecules.
RCOOH + HOR' ↔ RCOOR' + H2O with H2SO4 as catalyst
CH3COOH + HOC2H5 ↔ CH3COOC2H5 + H2O with H2SO4 as catalyst
The reaction is reversible is nature. Double headed arrow is used to indicate it. The equilibrium can be shifted toward the forward direction by removing water as soon as it is formed.
If dry HCL gas is used as a catalyst, the reaction is called Fisher=Speier esterification.
It is is difficult to prepare esters of tertiary alcohols becasue bulky groups in the alcohol decrease rate of reaction or esterification. This is termed as stearic hindrance of bulky groups.
As noted above in the reactions, esterification involved the cleavage of the O-H bonds of the alcohol. This was proved by using alcohol with isotopic O18 which can be tracked using isotopic tracer technique. It was found that this oxygen is present in the resulting ester which means that the oxygen in the alcohol is going into the ester and hydrogen is going into the water molecules.
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Dehydration
When alcohols are heated with conc. or H3PO4, at 443 K, they get dehydrated to form alkenes.
The ease of dehydration of alcohol follows the order 3>2>1 which is also the order of stability of carbocation.
When alcohols are heated with conc. or H3PO4, at 443 K, they get dehydrated to form alkenes.
The ease of dehydration of alcohol follows the order 3>2>1 which is also the order of stability of carbocation.
Dehydration of alcohols to ethers or alkenes can also be brought about by passing the vapour of the alcohols over heated alumina catalyst under different conditions
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Oxidation
The oxidation of alcohols can be carried out by a number of reagents such as acqueous, alkalineor acidified KMnO4, acidified Na2Cr2O7, nitric acid, chromic acid, etc.
Different classes of alcohols differ from each other in their ease of oxidation and also give different products.
(i) Primary alcohols: Primary alcohols are easily oxidized. First an aldehyde is formed and then from it carboxylic acid is formed. Both the aldehyde and the resulting acid contain the same number of carbon atoms as the starting alcohol.
(ii) Secondary alcohols: Ease of oxidation is still there. But they are oxidized to ketone and under strong conditions they are further oxidized to form a mixture of acids. While the ketone contains the same number of carbon atoms as the starting alcohol, the acids formed contain lesser number of carbon atoms.
(iii) It is difficult to oxidize tertiarly alcohols.
When treated with acidic oxidizing agents under very strong conditions they form first ketones and then acids.
Both the ketones and acids contain lesser number of carbon atoms than the starting alcohols.
The oxidation of alcohols can be carried out by a number of reagents such as acqueous, alkalineor acidified KMnO4, acidified Na2Cr2O7, nitric acid, chromic acid, etc.
Different classes of alcohols differ from each other in their ease of oxidation and also give different products.
(i) Primary alcohols: Primary alcohols are easily oxidized. First an aldehyde is formed and then from it carboxylic acid is formed. Both the aldehyde and the resulting acid contain the same number of carbon atoms as the starting alcohol.
(ii) Secondary alcohols: Ease of oxidation is still there. But they are oxidized to ketone and under strong conditions they are further oxidized to form a mixture of acids. While the ketone contains the same number of carbon atoms as the starting alcohol, the acids formed contain lesser number of carbon atoms.
(iii) It is difficult to oxidize tertiarly alcohols.
When treated with acidic oxidizing agents under very strong conditions they form first ketones and then acids.
Both the ketones and acids contain lesser number of carbon atoms than the starting alcohols.
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Reaction with sodium
The cleavage in this reaction will be in the OH bond. Alcohols react with active metals to liberate hydrogen gas an form metal alkoxide.
Ethanol or Ethyl alcohol reacts with sodium to gibve Sodium ethoxide and hydrogen
This reaction shows that alcohols are acidic in nature.
The acidic nature is due to the presence of polar O-H bond.
Alcohols are weak acids even weaker than water.
Reaction with phosphorus halides
Phosphorus halides such as PCl5, Pcl3, PBr3 and PI3 react with alcohols to form corresponding haloalkanes.
Haloalkanes : Chloroethane, Bromoethane, Iodoethane
Reaction with ZnCl2/conc.-HCl
This is a reaction or test to distinguish various categories of alcohols and is termed Lucas test.
In this test, an alcohol is treated with an equimolar mixture of concentrated hydrochloric acid and anhydrous ZnCl2 (called Lucas reagent).
Alcohols get converted into alkylhalides. As alkyl halides are insoluble in water, their presence is indicated by the appearance of turbidity in the reaction mixture.
The time required for the formation of alkyl halides and appearance of turbidity is very less in the tertiary alcohols.
in the case of secondary alcohols, it takes five minutes.
A primary alcohol produces turbidity only after heating.
Thus alcohols can be distinguished using Lucas test.
Conversion of alcohols into aldehydes and ketones
This topic was already covered in the topic of oxidation.
Oxidation of primary alcohol gives aldehydes.
Oxidation of secondary alcohols gives ketones.
It is difficult to oxidize tertiary alcohols.
The cleavage in this reaction will be in the OH bond. Alcohols react with active metals to liberate hydrogen gas an form metal alkoxide.
Ethanol or Ethyl alcohol reacts with sodium to gibve Sodium ethoxide and hydrogen
This reaction shows that alcohols are acidic in nature.
The acidic nature is due to the presence of polar O-H bond.
Alcohols are weak acids even weaker than water.
Reaction with phosphorus halides
Phosphorus halides such as PCl5, Pcl3, PBr3 and PI3 react with alcohols to form corresponding haloalkanes.
Haloalkanes : Chloroethane, Bromoethane, Iodoethane
Reaction with ZnCl2/conc.-HCl
This is a reaction or test to distinguish various categories of alcohols and is termed Lucas test.
In this test, an alcohol is treated with an equimolar mixture of concentrated hydrochloric acid and anhydrous ZnCl2 (called Lucas reagent).
Alcohols get converted into alkylhalides. As alkyl halides are insoluble in water, their presence is indicated by the appearance of turbidity in the reaction mixture.
The time required for the formation of alkyl halides and appearance of turbidity is very less in the tertiary alcohols.
in the case of secondary alcohols, it takes five minutes.
A primary alcohol produces turbidity only after heating.
Thus alcohols can be distinguished using Lucas test.
Conversion of alcohols into aldehydes and ketones
This topic was already covered in the topic of oxidation.
Oxidation of primary alcohol gives aldehydes.
Oxidation of secondary alcohols gives ketones.
It is difficult to oxidize tertiary alcohols.
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