Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Hong Luen on December 19, 2005, 04:04:30 AM
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Hi all, I have problems in naming the attached compounds. I believe they are called butenyl-semi-benzene or so. Please kindly teach me how to name each of them correctly. Thank you very much.
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hi,
here is an attempt to name your compunds
for compound (23) it is: 3-((E)-But-2-enyl)-1,2,3,4,5-penta
methyl-6-methylene-cyclohexa-1,4-diene.
for compound (24) it is: 1-((E)-But-2-enyl)-2,3,4,5,6-penta
methyl-benzene.
for compound (25) it is: 1,2,3,4,5-Pentamethyl-6-(1-methyl-a
llyl)-benzene.
GSR
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Dear GSR,
1. What is meant by (E) in the 3-((E)-But-2-enyl)-?
Is (E)-3-(But-2-enyl)- the same as 3-((E)-But-2-enyl)-?
2. For #23, is it a must to put the methylene at position 6?
Is it because the methylene is unsaturated as compared to the five methyl groups?
Alternatively, is it because that gives the smallest number 1,4 for the cyclohexa-diene?
3. Can we name #25 as 1-(But-3-en-2-nyl)-2,3,4,5,6-pentamethylbenzene?
4. What is the structure of "semi-benzene"?
Thank you very much.
Hong Luen
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hi,
you are right perhaps.
the compound 25 can also be named as: 1,2,3,4,5-pentamethyl-6-(1-methylprop-2-enyl)benzene.
about the semi-benzene structures, as for as I know these are dimers(head-to-tail or head-to-head) of benzyl radicals. but I am not sure.
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1. What is meant by (E) in the 3-((E)-But-2-enyl)-?
In a nutshell, E-Z nomenclature stands for cis-trans one, every time there are alkenes with different groups. Instead of two couples of groups, you have different groups (3 or 4) with different 'importance' (you know what I mean, don't you?).
As you can see below, E is to trans as Z is to cis.
E comes from German entgegen, which means (more or less) 'contrary to'; Z from zusammen, 'together'.
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E/Z nomenclature is always better than cis/trans! E/Z will always get you to the right compound, but with cis/trans you need to know which groups are cis or trans to one another. With E/Z the priority is built in.
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I agree with you, movies. However, cis-trans nomenclature is still extremely common and it is good for simple alkenes with two couples of different substituents.
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I agree with you, movies. However, cis-trans nomenclature is still extremely common and it is good for simple alkenes with two couples of different substituents.
Very true. You can still use it for disubstituted alkenes and everyone will know what you are talking about. I always try to encourage the use of E/Z though, to avoid future confusion!
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Thanks for Albert's explanation on E/Z nonmenclature.
Back to naming of #25, I have question on the "1-methylprop-2-enyl" that GSR suggested.
If it is 1-methyl attached to propene, it should be a butene, isn't it?
Then, it should be a butenylbenzene.
???
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It's "1-methylprop-2-enyl" because with benzene derivatives you start the numbering from the carbon connected to the benzene ring.
If you consider it as a butene group it becomes 1-butene-3(1,2,3,4,5-pentamethylbenzene) which is a butene derivative.
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i don't think that E & Z have interference with 23
you can simply find carbon numcber one and start naming from there
following IUPAC rules
http://www.acdlabs.com/iupac/nomenclature/ (http://www.acdlabs.com/iupac/nomenclature/)
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Can we name compound #25 as 1-(But-3-en-2-nyl)-2,3,4,5,6-pentamethylbenzene?