In each of the following group of compounds, identify (using the corresponding l

Question

In each of the following group of compounds, identify (using the corresponding lowercase Roman numeral) the one with the:
For alkane names with more than 10 carbons click here.

a) heptane(i), 3-methylhexane(ii), nonane(iii)

largest heat of combustion
smallest heat of combustion
highest boiling point

b) icosane(i), pentacontane(ii), tridecane(iii)

largest heat of combustion
smallest heat of combustion
lowest boiling point

c) 2,3,4-trimethylhexane(i), nonane(ii), 3,4-dimethylheptane(iii)

largest heat of combustion
smallest heat of combustion
lowest boiling point

Explanation / Answer

a]

More the stability lesser the heat of combustion

Longer chain alkanes are typically more stable (relatively, based on the number of carbons) compared with a shorter chain alkane.

More branched alkanes are more stable that linear alkanes.

Longer the chain higher the boiling point and vice versa

Linear chains have boiling point higher than branched chains of same alkane

Based on above rules :

Nonane - Higher boiling point and low heat of combustion

Heptane - Largest heat of combustion

b] Icosane - C20H42 [linear chain]

Pentacontane - C50H102 [Linear]

Tridecane - C13H28 [ Linear]

Largest heat of combustion : Tridecane

Smallest heat of combustion - Pentacontane

Lowest boiling point - Tridecane

c]

Largest heat of combustion - Nonane

Smallest heat of combustion - 2,3,4-trimethylhexane

Lowest boiling point - 2,3,4-trimethylhexane

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