Question 1

What is the general formula for alkanes?

Accepted Answer

Alkanes are saturated hydrocarbons with only single C-C bonds, following the formula CnH2n+2 for acyclic compounds.

Question 2

Which of the following represents a primary alcohol?

Accepted Answer

A primary alcohol has the hydroxyl group (-OH) attached to a carbon bonded to only one alkyl group; CH3CH2OH fits this definition.

Question 3

What is the IUPAC name of the compound CH3-CH2-CH2-CH3?

Accepted Answer

This straight-chain hydrocarbon contains 4 carbon atoms, making it butane according to IUPAC nomenclature.

Question 4

Identify the functional group present in CH3COCH3.

Accepted Answer

CH3COCH3 contains a carbonyl group (C=O) bonded to two alkyl groups, which defines a ketone.

Question 5

Which pair of compounds represents isomers?

Accepted Answer

Both CH3CH2CH3 (n-propane) and CH3CH(CH3)2 (isopropane) have the molecular formula C3H8, making them constitutional isomers.

Question 6

What is the general molecular formula for a saturated acyclic alkane containing 5 carbon atoms?

Accepted Answer

Saturated acyclic alkanes follow the formula CₙH₂ₙ₊₂; for n=5, this gives C₅H₁₂ (pentane).

Question 7

Which of the following represents the correct definition of isomerism in organic chemistry?

Accepted Answer

Isomers have identical molecular formulas but differ in structural arrangement, leading to different properties.

Question 8

In the IUPAC nomenclature system, the principal functional group in an alcohol is indicated by which suffix?

Accepted Answer

The suffix '-ol' is used in IUPAC nomenclature to denote the hydroxyl (-OH) functional group in alcohols.

Question 9

What is the hybridization state of the carbon atom in a methane (CH₄) molecule?

Accepted Answer

Carbon in methane forms four sigma bonds with hydrogen using sp³ hybridization, resulting in a tetrahedral geometry.

Question 10

Which type of structural isomerism occurs when the atoms are arranged in a different order within the carbon chain?

Accepted Answer

Chain isomerism arises when carbon atoms form chains of different structures while maintaining the same molecular formula.

Question 11

The degree of unsaturation in a compound with molecular formula C₆H₁₀O is:

Accepted Answer

Degree of unsaturation = (2C + 2 + N - H - X)/2 = (12 + 2 - 10)/2 = 2, indicating two double bonds or one ring plus one double bond.

Question 12

Which of the following statements about covalent bonds in organic molecules is correct?

Accepted Answer

A triple bond (C≡C) comprises one sigma bond formed by end-on overlap and two pi bonds formed by side-on overlap of p-orbitals.

Question 13

In the combustion of ethane (C₂H₆), the balanced chemical equation is:

Accepted Answer

Complete combustion of C₂H₆ produces 2 moles of CO₂ and 3 moles of H₂O, requiring 3.5 or 3 moles of O₂ when expressed as C₂H₆ + 3O₂.

Question 14

Which of the following compounds exhibits the highest degree of unsaturation (DBE) with molecular formula C₅H₆O₂?

Accepted Answer

Degree of unsaturation = (2C + 2 - H)/2 = (10 + 2 - 6)/2 = 3, indicating three degrees of unsaturation (rings and/or double bonds combined).

Question 15

In a homologous series of alkanes, the difference in molecular mass between consecutive members is always:

Accepted Answer

Each successive alkane differs by one CH₂ unit, which has a mass of 12 + 2(1) = 14 u.

Question 16

A hydrocarbon CₙH₂ₙ₋₂ is most likely to be:

Accepted Answer

Formula CₙH₂ₙ₋₂ has DBE = 2, which corresponds to either one triple bond (alkyne) or one ring + one double bond; cycloalkene fits this with one ring and zero DBE from saturation, but the general formula indicates an alkene in a ring structure.

NDA Basic Organic Chemistry

Basic Organic Chemistry — Practice Questions