The Student Room Group
Reply 1
Velouria
If you dehydrated the following alcohol:

CH3CH2C(OH)(CH3)CH2CH2CH3 [3-methyl hexan-3-ol]

how many different alkenes could you produce? Would it just be:

3-methyl hexan-2-ene

and

4-methyl hexan-3-ene?


You need to take into consideration geometric isomerism.
Reply 2
Oh, ok. So I'd just have the cis and trans forms of each of the 2 alkenes, giving a total of 4 diff alkenes then?
Reply 3
Velouria
Oh, ok. So I'd just have the cis and trans forms of each of the 2 alkenes, giving a total of 4 diff alkenes then?


Yeah
Reply 4
Thanks.

One more question! Can CH3C(CH3)2CH2OH be dehydrated to form an alkene? I can't think where the double bond would form... :confused:
Velouria
Thanks.

One more question! Can CH3C(CH3)2CH2OH be dehydrated to form an alkene? I can't think where the double bond would form... :confused:


it cant be dehydrated to form an alkene as there is no H at the alpha position to the alkanol group
Velouria
If you dehydrated the following alcohol:

CH3CH2C(OH)(CH3)CH2CH2CH3 [3-methyl hexan-3-ol]

how many different alkenes could you produce? Would it just be:

3-methyl hex-2-ene

and

4-methyl hex-3-ene?


you would also produce 2-ethyl pent-1-ene (not entirely sure about the name) CH2=C(C2H5)CH2CH2CH3

yes that's the name -. when there is an alkene the longest chain that contains the double bond is chosen as the root

see http://chemistry.wlu.edu/WebPDF/241/241%2002/Alkene%20Nomenclature.pdf
Reply 7
Just wondering how is it possible to form geometrical isomers for both 3-methylhex-2-ene and 4-methylhex-3-ene? There is only one methyl and one H at each side of the double bond.
Reply 8
charco
you would also produce 2-ethyl pent-1-ene (not entirely sure about the name) CH2=C(C2H5)CH2CH2CH3

yes that's the name -. when there is an alkene the longest chain that contains the double bond is chosen as the root

see http://chemistry.wlu.edu/WebPDF/241/241%2002/Alkene%20Nomenclature.pdf



Oh i got it now. Thanks
3-methyl hex-2-ene CH3CH=C(CH3)CH2CH2CH3 has a methyl group either side of the double bond and has geometric isomers with both CH3 groups on the same side (cis), or trans to the d.b.

4-methyl hex-3-ene CH3CH2CH=C(CH3)CH2CH3 has an ethyl group either side of the double bond and has geometric isomers with both C2H5 groups on the same side (cis), or trans to the d.b.
Reply 10
charco
you would also produce 2-ethyl pent-1-ene (not entirely sure about the name) CH2=C(C2H5)CH2CH2CH3

yes that's the name -. when there is an alkene the longest chain that contains the double bond is chosen as the root

see http://chemistry.wlu.edu/WebPDF/241/241%2002/Alkene%20Nomenclature.pdf


Thank you muchly :smile:
Reply 11
Um I've forgotten how to do NMR Spec :redface:

E.g. In trans 2-methyl hex-2-ene would the following be correct:

6 peaks
Ratio 1:3:2:2:3:3
Singlet, doublet, singlet, triplet, triplet, singlet?
Velouria
Um I've forgotten how to do NMR Spec :redface:

E.g. In trans 2-methyl hex-2-ene would the following be correct:

6 peaks
Ratio 1:3:2:2:3:3
Singlet, doublet, singlet, triplet, triplet, singlet?


the height of the integral is equal to the number of carbons

the splitting pattern is equal to the number of adjacent carbons +1

2-methyl hex-2-ene is CH3C(CH3)C=CHCH2CH3

on the left hand side [CH3C(CH3)C] you have 6 equivalent hydrogens these will give a peak with an integral = 6
then you have one hydrogen (integral =1) adjacent to a CH2 group which will be split into a triplet. The CH2 group itself will have an integral = 2 and be split by its neighbouring CH3 into a quartet (which in turn will we be doubleted by the CH on the other side).
it's late and I'm bored now but do you get the idea?