Topic 3.2: Functional Groups — Classification of Organic Compounds Questions

Glucose has the molecular formula C₆H₁₂O₆.

Deduce its empirical formula.

State the general formula of the homologous series of alkanes, and explain why successive members differ by CH₂. [2]

A flavouring molecule has a four-carbon chain with a –COOH group at one end.

Identify the functional group present and state the class of compound, then deduce its IUPAC name. [2]

A molecule has a four-carbon chain with a chlorine atom on the second carbon and no other functional groups.

Deduce its systematic (IUPAC) name. [2]

Pentane has the molecular formula C₅H₁₂.

Draw the structural formula of one structural isomer of pentane and explain why it is an isomer.

An unknown liquid has the molecular formula C₂H₆O.

Its mass spectrum shows the molecular ion at m/z = 46 and a strong peak at m/z = 31; its infrared spectrum has a broad absorption at 3340 cm⁻¹; its ¹H NMR spectrum shows three peaks.

Deduce the structure of the compound, referring to all three spectra. [3]

But-2-ene has the molecular formula C₄H₈.

Deduce whether it is saturated or unsaturated, and state the general formula of the homologous series it belongs to. [2]

Hex-2-ene, CH₃CH=CHCH₂CH₂CH₃, exists as two stereoisomers, but hex-1-ene, CH₂=CHCH₂CH₂CH₂CH₃, does not.

Explain this difference, naming the type of isomerism involved. [3]

Propan-2-ol, CH₃CH(OH)CH₃, can be made from propene, CH₃CH=CH₂, in two steps.

Deduce the reagents and conditions for each step, name the intermediate, and state the type of each reaction. [4]

Butan-2-ol, CH₃CH(OH)CH₂CH₃, shows optical isomerism, but 2-methylpropan-2-ol, (CH₃)₃COH, does not.

Explain why, and state how the two optical isomers of butan-2-ol differ in their behaviour. [3]

Benzene, C₆H₆, is more stable than would be expected for a molecule with three carbon–carbon double bonds.

(a) Describe the bonding in benzene.

(b) Explain how the enthalpy of hydrogenation provides evidence for this extra stability. [4]

A compound with formula C₃H₆O shows its molecular ion at m/z = 58 and a base peak at m/z = 43, a sharp infrared absorption at 1715 cm⁻¹ and no absorption above 3000 cm⁻¹, and a single peak in its ¹H NMR spectrum.

Identify the compound and explain how the spectra support your answer. [3]