Classification, Nomenclature And Isomerism.pdf 21n44

Mr. V. T. Pawar, Asst.Prof., Pharmaceutical Chemistry Department Bharati Vidyapeeth College of Pharmacy, Kolhapur.

Compound

Organic Compound

 The compounds in solid, liquid or gaseous state which contain carbon in its molecule are known as organic compounds.  There are a large number of organic compounds and therefore a proper systematic classification was required.

Organic Compounds Closed Chain or Cyclic

Open Chain or Alicyclic

Straight Chain

Branched Chain

Homocyclic/Carbocylic Compounds

Alicyclic

Benzenoid Compounds

Aromatic

Heterocyclic

Alicyclic

Nonbenzenoid Compounds

Aromatic

Acyclic or open chain compounds: • Terminal carbon atoms are free & they are not linked to each other so called open chain compounds or acyclic compounds. • These compounds are also known as aliphatic compounds, they have branched or straight chains.

Straight chains Butane

Branched chains

Closed chain or ring compounds: • These compound contains one or more closed chain or ring of atoms in their molecules. • Terminal carbons of the compound, They are linked with each other in order to form closed ring so we called them as closed chain compounds or ring compounds.

• These are again devided in to two class  Homocyclic compounds  Heterocyclic compounds

Homocyclic or Carboxylic Compounds • These compound contains ring which are made up of atoms of one kind (i.e. Carbon atoms only.

• These compound Classified in to two class  Alicyclic Compounds  Aromatic Compounds

Alicyclic Compounds  These are the compounds which resemble aliphatic compounds in most of their properties.

Cyclobutane

Aromatic Compounds  These are the carbocyclic compounds which contain alternate double and single bonds between the carbon atoms.

Aromatic Compounds • Aromatic Compounds are again classified in to two class  Benzenoid Compounds  Non-benzenoid Compounds Benzenoid Compounds:  Organic compounds containing one or more fused benzene rings.

Nonbenzenoid Compounds:  Aromatic compounds which do contain benzene rings.

Azulene

Heterocyclic Compounds • These compounds contain rings made up of one or more atoms of nitrogen, oxygen, sulphur etc., in an addition to carbon atoms.

• These are again classified in to two class  Alicyclic Compounds  Aromatic Compounds

Alicyclic Compounds • Aliphatic cyclic compounds containing one or more heteroatoms in their rings.

Tetrahydrofuran

Tetrahydropyrrole

Tetrahydrothiopene

Aromatic Compounds • Aromatic cyclic compounds containing one or more heteroatoms in their rings.

Isomerism is the phenomenon of exhibiting two or more compounds with same molecular formula but different physical and chemical properties. Isomers are the compounds showing different physical and chemical properties but same molecular formula.

The isomerism in organic compounds can be classified broadly into: Structural isomerism (constitutional isomerism)

Stereo isomerism [email protected]

CHAIN ISOMERISM

POSITION ISOMERISM

STRUCTURAL ISOMERISM

FUNCTIONAL GROUP ISOMERISM

Same molecular formula but different structural formulae METAMERISM

TAUTOMERISM

STEREOISOMERISM Same molecular formula but atoms occupy different positions in space.

GEOMETRICAL ISOMERISM Occurs due to the restricted rotation of C=C double bonds... two forms CIS and TRANS OPTICAL ISOMERISM

Occurs when molecules have a chiral centre. Get two non-superimposable mirror images.

STRUCTURAL ISOMERISM

Same molecular formula but different structural formulae

CHAIN ISOMERISM The chain isomerism arises due to different arrangements of carbon atoms leading to linear and branched chains.

The chain isomers have same molecular formula but different types of chains i.e., linear and branched. The chain isomers have almost similar chemical properties but different physical properties. For example, the branched chain isomers have lower boiling points than that of their linear counterparts. It is because, the linear ones have more surface area of and hence the intermolecular forces of attraction are maximum. Two chain isomers possible with the molecular formula, C4H12. i.e., n-butane: a linear chain isomer. isobutane (or 2-methylpropane): a branched isomer

POSITION ISOMERISM The positional isomerism arises due to different positions of side chains, substituents, functional groups, double bonds, triple bonds etc., on the parent chain. E.g. 1) Propyl chloride and isopropyl chloride are the positional isomers with the molecular formula, C3H7Cl. These isomers arise due to difference in the position of the chloro group on the main chain.

2) In the following positional isomers i.e., but-1-ene and but-2-ene the position of double is different but they have same molecular formula, C4H8.

POSITION ISOMERISM 3) The functional group, -OH is at different positions on the main chain of the following alcohols. They have the same molecular formula, C3H7OH.

4) In the following positional isomers i.e., ortho xylene, meta xylene and para xylene, the relative positions of methyl groups on the benzene ring are different

FUNCTIONAL GROUP ISOMERISM The functional isomerism arises due to presence of different functional groups. The functional isomers have the same molecular formula but possess different functional groups. The functional isomers show different physical as well as chemical properties.

E.g. 1) The dimethyl ether is the functional isomer of ethyl alcohol. Both have the same molecular formula, C2H6O. However they have different functional groups.

2) Acetaldehyde is a functional isomer of acetone. They have the same molecular formula, C3H6O but different functional groups. Acetaldehyde contains aldehyde, -CHO functional group, whereas acetone has ketone, >C=O functional group.

FUNCTIONAL GROUP ISOMERISM

3) Both Acetic acid and methyl formate are also functional isomers. They have the same molecular formula, C2H4O2. Acetic acid is a carboxylic acid with -COOH group whereas methyl formate is an ester with -COOCH3 group.

METAMERISM  The metamerism arises when different alkyl groups are attached to same functional group. E.g. 1) The following metamers contain the ether functional group. However they differ by the nature of alkyl groups attached to the oxygen atom.

2) The metamerism is also possible in amines as shown below.

TAUTOMERISM Tautomerism refers to the dynamic equilibrium between two compounds with same molecular formula. It is also called as desmotropism or kryptotropism or prototropy or allelotropism. It is most often a special case of functional group isomerism. In general, the tautomers have different functional groups and exist in dynamic equilibrium with each other due to a rapid interconversion from one form to another. It is very important to note that the tautomers are not the resonance structures of same compound. Tautomerism consist of two types:

1) Keto-enol tautomerism: 2) The nitro-aci tautomerism:

1) Keto-enol tautomerism: The carbonyl compounds containing at least one α-hydrogen atom exhibit keto-enol tautomerism. The carbonyl group can be converted to enol form due to transfer of one of the α-hydrogen onto the oxygen atom. Note: An alcoholic group on C=C is called enol. It is an alkene alcohol. The % composition of keto enol tautomeric mixture depends on the relative stabilities of these two forms. In general the keto form is the low energy form and is more stable than the enol form. However the enol form is also stable in certain cases due to other stability factors. The dynamic equilibrium between a keto form and an enol form exhibited by acetone is shown below. The tautomers are formed due to complete transfer of hydrogen. However the relatively stable keto form exists in higher percentage (about 99%).

 However enol form is also appreciably stable in case of 1,3-dicarbonyl compounds like acetoacetic ester (ethyl aceto acetic ester) as depicted below.

 The enol form is more stable than the keto form in case of phenols due to resonance stabilization of aromatic ring.

2) The nitro-aci tautomerism:

 It is exhibited by nitro compounds containing at least one α-hydrogen. In this case also, the hydrogen atom is transferred completely from one atom to another during the conversion of nitro form to aci form and vice versa.

E.g. The nitro-aci tautomerism exhibited by nitromethane is shown below.

IUPAC: International Union of Pure and Applied Chemistry

1. Carbon Chain/Word Root/Principle Chain 2. Functional Group Chain Length

Word Root

Chain Length

Word Root

1C

Meth

6C

Hex

2C

Eth

7C

Hept

3C

Prop

8C

Oct

4C

But

9C

Non

5C

Pent

10 C

Dec

Functional Group: Group which decide the chemical properties of organic compounds

Main Functional Group (Suffix name) Functional Group: Substituent Functional Group (Prefix Name)

OH

CH3

H H3C C C C CH3 H H2 Cl Br Word Root- 6 carbon Chain Functional Group: OH, CH3, Cl, Br. Main Functional Group: -OH Substituent Functional Groups: CH3, Cl, Br.

OH H3C

C H

H C

CH3

Cl Br

C CH3 H2

Word Root- 6 carbon Chain Functional Group: OH, CH3, Cl, Br. Main Functional Group: -OH Substituent Functional Groups: CH3, Cl, Br.

4-Bromo-3-Chloro-4-methylhexan-2-ol

S-Substituent, P-Principle Chain, P-Primary Suffix, M-Main Functional Group

H2 H3C C C H2 CH2 CH3 2-Methyl Pent-1-ene

H H H3C 3 C 4C CH3 5

2

CH2CH2

1

CH3CH3 6

3,4-dimethyl hexane

H H H3C5 C C3 C 2 CHO 4 1 H2 OH CH3 Sub Sub

4-Hydroxy 2-Methyl Pentane-al

4-Hydroxy 2-Methyl Pentan-al

MFG

5

CH3

HO 4 C C 3 H H2

CH3

1 2

OH

CH3 Sub

2-Methyl Pentane -2,4-Diol

MFG

CH3

SUB

SUB

H 1C 2C 3CH3 H NH2 MFG

2-Methyl-1-Phenyl Propane-1-amine

2-Methyl-1-Phenyl Propanamine