Question

Q2: Which molecule would be expected to expect the highest boiling point as a pure substance that are molecular isomers with the same molecular formula, C5H12? 10 vs 40 0C.

- neopentane ( Hint: (CH3)4 C )

Answer 1

₄hydrocarbon C5 H12 has three molecular isomers ie.

1 ) CH3-CH2 -CH2-CH2 -CH3 a straight chain compound ( n -Pentane )..............Boiling point----- 40^o C

2 ) CH3 CH (CH3) CH2 CH3 , an isomer with only one branch (2-methyl butane )

3 ) C (CH3) ₄ , an isomer with two branches ( 2,2 dimethyl propane or neopentane ) ------- Boiling point ----- 10^o C

n-Pentane with NO branching would have highest Boiling Point ...........40^o C

Explaination :-

It is because branching in the structures of isomeric compounds / molecules causes a decrease in surface area . This decrease in surface area of the molecule reduces inter -molecular forces also, resulting into lower boiling points of branched chain isomers.