What compound has a higher melting point?

Question

1-propanol ..... CH3CH2CH2OH
1-heptanol ..... CH3CH2CH2CH2CH2CH2CH2OH

I said 1-propanol because it's intermolecular forces are stronger, due to its shorter chain (which over-rides 1-heptanol's stronger dispersion forces). Am I right?

Oh. My. God.

I meant boiling point!!!

My bad.

Answer 1

It ought to be the heptanol.

As molecules increase in size, intermolecular forces also increase. This raises the melting point. Alcohols are influenced by the hydrogen bonds formed by the hydroxyl group. This makes ethanol a liquid, but ethane is a gas. As the length of the hydrocarbon chain increases, intermolecular attractions between hydrogen atoms begin to influence the properties of the compound. These are known as van der vall's forces and although not as strong as hydrogen bonds, they can accumulate, especially if there are lots of hydrogen atoms. This is why hydrocarbons like methane are gasses, hexane is a liquid and as the chain increases in length, the vicosity and melting point increase. The extreme example is the plastic polyethylene, which has a hydrocarbon chain hundreds of units long.

Answer 2

heptanol will have stronger intramolecular forces however!

Other factors will play a role, but it is INTRAmolecular forces that sway the mp factor the most (in my opinion).

Like the first reply, obviously n-hexanol is the higher mp over 1-propanol. 1-heptanol will have a slightly higher mp than 1-hexanol.

Answer 3

Melting points:

1-propanol = -126.5 C
1-heptanol = -34.6 C

Heptanol has a higher mpt.

Answer 4

Generally longer molecules have higher melting and boiling points. So, I would go for 1 - heptanol

Answer 5

1-propanol mp= -126
1-hexanol mp= -52C

long chains are like thick oils
heptanol really isnt all that thick yet, but still the principle applies, usually longer chains are higher bp

Answer 6

propanol b

Answer 7

propanol