(SEM II) THEORY EXAMINATION 2017-18 PHARMACEUTICAL ORGANIC CHEMISTRY I

SECTION A – Short Answer Section

This section contains basic conceptual questions related to organic chemistry fundamentals. Students must answer briefly. The questions mainly test knowledge about chemical structures, hybridization, nucleophiles, and basic organic reactions used in pharmaceutical chemistry.

Question 1: What are Chiral and Achiral Compounds?

Answer:
A chiral compound is a molecule that cannot be superimposed on its mirror image. These compounds usually contain a chiral carbon (asymmetric carbon) attached to four different groups.
Example: Lactic acid.

An achiral compound is a molecule that can be superimposed on its mirror image and does not contain an asymmetric carbon atom.

Question 2: What is Hybridization?

Answer:
Hybridization is the mixing of atomic orbitals of similar energy to form new hybrid orbitals that are equal in energy and shape.

Types of hybridization include:

sp hybridization

sp² hybridization

sp³ hybridization

For example, carbon in methane (CH₄) shows sp³ hybridization.

Question 3: What is a Nucleophile?

Answer:
A nucleophile is a chemical species that donates an electron pair to form a new covalent bond.

Examples of nucleophiles include:

OH⁻ (hydroxide ion)

NH₃ (ammonia)

Cl⁻ (chloride ion)

Nucleophiles are important in substitution and addition reactions in organic chemistry.

SECTION B – Long Answer Section

This section requires students to explain organic reaction mechanisms and chemical processes in detail. Questions usually focus on reaction types, preparation methods, and reaction kinetics.

Question 1: Differentiate between E1 and E2 reactions.

Answer:

E1 reactions usually occur in tertiary alkyl halides, while E2 reactions occur in primary and secondary alkyl halides.

Question 2: What are SN1 and SN2 reactions?

Answer:

SN1 Reaction (Substitution Nucleophilic Unimolecular):

Occurs in two steps.

Formation of carbocation intermediate.

Rate depends only on substrate concentration.

SN2 Reaction (Substitution Nucleophilic Bimolecular):

Occurs in one step.

No carbocation intermediate.

Rate depends on both nucleophile and substrate.

SN2 reactions involve backside attack, leading to inversion of configuration.

Question 3: What are Carbonyl Compounds?

Answer:
Carbonyl compounds are organic compounds containing the carbonyl group (C=O).

Types include:

Aldehydes (R-CHO)

Ketones (R-CO-R)

Preparation methods:

Oxidation of alcohols

Ozonolysis of alkenes

Hydration of alkynes

Carbonyl compounds are highly reactive because of the polar nature of the C=O bond.

SECTION C – Descriptive Section

This section tests detailed understanding of organic reaction mechanisms, rules, and chemical classifications used in pharmaceutical chemistry.

Question 1: Explain Markovnikov and Anti-Markovnikov Rule.

Answer:

Markovnikov Rule:
When a hydrogen halide (HX) adds to an unsymmetrical alkene, the hydrogen atom attaches to the carbon with more hydrogen atoms, and the halide attaches to the carbon with fewer hydrogen atoms.

Example:
Propene + HBr → 2-Bromopropane

Anti-Markovnikov Rule:
In the presence of peroxides, the addition of HBr occurs in the opposite direction.

Example:
Propene + HBr (peroxide) → 1-Bromopropane

Question 2: Explain sp³ Hybridization in Alkanes.

Answer:
In alkanes, carbon atoms undergo sp³ hybridization, where one s orbital mixes with three p orbitals to form four sp³ hybrid orbitals.

Characteristics:

Tetrahedral geometry

Bond angle of 109.5°

Formation of strong sigma bonds

Example: Methane (CH₄).

Question 3: Explain the Cannizzaro Reaction.

Answer:
Cannizzaro reaction is a disproportionation reaction in which aldehydes without alpha-hydrogen react with a strong base to produce an alcohol and a carboxylic acid.

Example:
2HCHO + NaOH → HCOONa + CH₃OH

This reaction is important in organic synthesis for producing alcohols and acids.