C6H10 has a ring structure. Hydrogenation of this gives C6H12, which does not react with aqueous Bromine why?

Question

Also, why would the C6H12 have a ring structure?

Any help appreciated.
Many Thanks.

The bit about the ring, i think it wants an explanation... explain why C6H12 must have a ring structure?

Answer 1

C6H12 is HEXENE, and has to form a ring (sketch it). It is also hydrophobic, and therefore is non-polar, so it can't react with the polar Bromine (aq).

Answer 2

First you need to find out the degree of unsaturation of C6H10
An aliphatic saturated alkane would have the genral type
CnH2n+2.
Howewer you know that it is a cyclic compound. Thus you need to substract 2 H from the formula to account for the C-C bond that will close the ring. So for a saturated cycloalkane you should have CnH2n, or in this case C6H12. You have 2 H atoms less, meaning that C6H10 has a double bond.

When you do the hydrogenation, 2H atoms are added to the double bond and you get C6H12. The ring structure pre-existed in C6H10 and is not affected by the hydrogenation reaction.

Since it is C6H12 is saturated it doesn't react with aqueous Bromine. C6H10 would have reacted giving 1,2-dibromo-cyclohexane (it woud have been exactly like the hydrogenation reaction with the only difference being that you have 2 Br added to the C atoms of the double bond instead of 2 H)

Answer 3

From the formula C6H10, one can calculate the 'degree of unsaturation'. The formula CnH(2n+2), this tells you that the saturated C6-hydrocarbon (hexane) is C6H14. Every two hydrogen atoms below this means one degree of unsaturation. Thus, C6H12: 1 degree; C6H10: 2 degrees; C6H8: 3 degrees etc.
So there are 2 degrees of unsaturation, which could mean:
(a) two double-bonds; (b) two rings; (c) one double bond and one ring; (d) a triple bond.

Since we are TOLD that it has a ring structure, it must be either (b) or (c). Since it can be hydrogenated, there must be at least one double bond. Hence, it must be either (a) or (c). Combining these two inferences means that it must be option (c): one ring and one double bond.

If C6H10 has one ring and one double bond, there are a number of things it could be. The most obvious is cyclohexene, but it could also be methylcyclopentene, dimethylcyclobutene, ethylcyclobutene etc. Or the double bond could be on the side-chain, e.g. vinylcyclobutane. Hydrogenation will add hydrogen across the double bond, converting it to a single bond. Thus cyclohexene will give cyclohexane, dimethylcyclobutene will give dimethylcyclobutane etc.

Aqueous bromine reacts with those hydrocarbons that contain at least one double bond (or triple bond), but will not react with hydrocarbons in which all the carbon-carbon bonds are single. Aqueous bromine will not react with the C6H12 in question, as it does not contain any carbon-carbon double bonds.

Answer 4

The first has a double bond but the second doesn't. Bromine reacts across a double bond.

You are right that C6H12 could be a straight chain alkene (hexene) but if it is formed from hydrogenation of C6H10 (cyclohexene) it must be cyclohexane. Whish I could draw structures on here it would make it much simpler.

Answer 5

You say that it is cyclic.

If C6H10 is an unsaturated cyclo-alkene with 1 double bond it is called cyclo-hexene. cy-C6H10

Because of the double bond it is reactive.

Hydrogenation forms a saturated alkane, cyclo-hexane which is not reactive.

C6H12 does not necessarily indicate a cyclic structure.

It could be a straight chain olefin with 1 double bond - 'Hexene'.

Apologies, C6H10 does imply cyclic structure. Normal Hexene would be C6H12. Thank you 'thesmileyman' and you're right about structures - other fonts would be useful too.

Answer 6

This is very sketchy a level chem, but I think c6h10 must have an unsaturated c-c double bond, which will be attacked by the -ve bromide ion. The saturated c6h12 molecule (cyclohexane) has no such bonds and as such is stable enough to withstand -ve ion attack. I think thats roughly right, but I wouldnt hand it in as my homework answer!

Answer above incorrect. Benzene is c6h6. It contains 3 c-c double bonds.

Above answer corrected. A typo, perhaps.

Answer 7

C6H12 is saturated,ie has no double or triple bonds.C6H10 has one double bond and accepts a hydrogen molecule.C6H12 has a ring structure because it is the conformation which suits the bonding.