organic chemistry 1st year solved exercise

Chapter 15 Solved Exercise Organic Chemistry

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Organic Chemistry Federal board

Explore comprehensive chemistry resources for Federal Board students! This section covers essential topics like functional groups, alkyl groups, isomerism, reaction mechanisms, homologous series, and bond fissions. With detailed explanations, structural formulae, and solved exercises, students can deepen their understanding of organic chemistry concepts and prepare effectively for exams. Perfectly tailored for Federal Board college students, these resources simplify complex topics with clear examples and systematic solutions.

Detailed Solutions for College Students (Federal Board, Islamabad)

1. Importance of Functional Groups

Functional groups are specific groups of atoms within molecules responsible for their chemical properties and reactions. They determine the reactivity, solubility, and physical properties of a compound. For example:

  • Hydroxyl group (-OH): Present in alcohols, makes compounds polar and soluble in water.
  • Carbonyl group (-C=O): Present in ketones and aldehydes, critical in organic reactions like nucleophilic addition.

2. Alkyl Group

An alkyl group is a hydrocarbon fragment derived by removing one hydrogen atom from an alkane. Its general formula is ( C_nH_{2n+1} ).

Alkyl Groups from Isomers of Propane:

  1. Propyl (CH3CH2CH2)
  2. Isopropyl (CH3CHCH3)

Alkyl Groups from Isomers of Butane:

  1. Butyl CH3CH2CH2CH2-
  2. Isobutyl (CH3CH(CH3)CH3)
  3. Sec-butyl CH3CH(CH3)CH2-
  4. Tert-butyl C(CH3)3-

3. Systematic Names for Compounds

i. CH3CH2COCl: Propanoyl chloride
ii. CH3CN: Ethanenitrile
iii. CH3OCH3: Methoxymethane (Dimethyl ether)

4. Correction of Wrong Names

a. 1-methylpentane:

  • Correct structure: This name is invalid because a methyl group cannot be attached to the first carbon of pentane.
  • Correct name: Hexane

b. 2-ethylbutane:

  • Correct structure: This name is invalid because the longest chain would be pentane.
  • Correct name: 3-methylpentane

c. 2-methylcyclohexane:

  • Correct structure: Valid name.

d. 3,3-methyl-4-ethylheptane:

  • Correct structure: This name is invalid because substituents must be numbered with the lowest possible set of numbers.
  • Correct name: 3-ethyl-4,4-dimethylheptane

5. Electrophiles and Nucleophiles

  • Electrophile: Electron-deficient species that accepts electrons during a reaction. Examples: ( H+ ), ( NO2+ ).
  • Nucleophile: Electron-rich species that donates electrons during a reaction. Examples: ( OH– ), ( CN– ).

6. Chain Isomerism, Metamerism, and Positional Isomerism

  • Chain Isomerism: Compounds with the same molecular formula but different arrangements of the carbon chain.
    Example: n-butane and isobutane (C4H10).
  • Metamerism: Compounds with the same molecular formula but different alkyl groups on either side of a functional group.
    Example: ( CH3OCH2CH3 ) and ( CH3CH2OCH3 ).
  • Positional Isomerism: Compounds with the same molecular formula but different positions of a functional group.
    Example: ( CH3CH2OH ) and ( CH3OCH3 ).

7. Structural Isomers of C4H9Br

  1. 1-bromobutane
  2. 2-bromobutane
  3. 1-bromo-2-methylpropane
  4. 2-bromo-2-methylpropane

8. Aliphatic Compounds

Aliphatic compounds are organic compounds with straight or branched chains.
Examples: Methane (CH4), Ethane (C2H6).

9. Skeletal vs. 2D Displayed Structural Formulae

  • Skeletal Formula: Simplified representation showing only bonds between carbon atoms.
  • 2D Displayed Formula: Shows all bonds and atoms explicitly.

Examples:

  1. Methane: ( CH_4 )
  2. Ethanol: ( CH_3CH_2OH )

10. Molecular Formula of Compound

Given: Molecular mass = 26 amu, Empirical formula = CH.

  • Empirical mass = 12 (C) + 1 (H) = 13 amu.
  • Molecular formula = ( CH X 2 = C2H2 ).

11. Homologous Series

A homologous series is a group of organic compounds with the same functional group and similar chemical properties but differing by a CH2 unit.
Features:

  • Gradual change in physical properties.
  • Same general formula.
  • Similar chemical properties.

12. Free Radical Substitution Reaction

Definition: A reaction where a free radical replaces a hydrogen atom.
Example: Bromination of methane:

13. Nucleophilic Substitution and Electrophilic Addition

  • Nucleophilic Substitution: Replacement of a leaving group by a nucleophile. Example: Hydrolysis of alkyl halides.
  • Electrophilic Addition: Addition of an electrophile to a double or triple bond. Example: Bromination of ethene.

14. Structural Isomerism

  • Functional Group Isomerism: Compounds with the same molecular formula but different functional groups. Example: ( CH3OH ) and ( CH3OCH3 ).
  • Tautomerism: Dynamic equilibrium between structural isomers. Example: Keto-enol tautomerism.

15. Homolytic and Heterolytic Fission

Halogenation of Alkanes:
Homolytic fission produces free radicals, initiating the substitution of hydrogen atoms in alkanes with halogens.

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