Alkanes cannot have cis/trans isomerism because:?

👨🏻‍🏫 學術台化學

[匿名]

2017-09-11 10:26 am

A. alkanes only have carbon and hydrogen atoms.
B. all of the bonds in an alkane freely rotate.
C. the carbon-carbon bonds in alkanes do not freely rotate.
D. the carbon-hydrogen bonds in alkanes freely rotate.

I chose B and D as my answers, and both were incorrect. Is A the answer? My textbook mostly talks about bonds when discussing cis-trans isomers, so I didn't think that the atoms present in alkanes were more important than the bonds in regards to cis-trans isomers.

更新1:

Thank you everyone! I submitted "b" as my answer again and received credit.

回答 (3)

[匿名]

2017-09-11 11:12 am

✔ 最佳答案

First of all, you have to know why cis/trans isomerism is formed. It is known that C=C double bond cannot freely rotate, and thus the spatial arrangement of the 4 certain group(s)/atom(s) may form 2 different compounds known as cis/trans isomers.

Therefore, a basic condition for the occurrence of cis/trans isomerism is that the compound contains at least one C=C double bond which cannot freely rotate. Alkane contains only C-C and C-H single bonds, and all of them can freely rotate. Therefore, alkanes cannot have cis/trans isomerism.

The answer: B. all of the bonds in an alkane freely rotate.

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az_lender

2017-09-11 10:32 am

B is correct. Maybe if you marked two answers, they automatically told you that you were incorrect. D is true, but it's not the reason why alkanes can't have cis/trans isomers.

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[匿名]

2017-09-11 10:58 am

A Hydrogen atom is as close to a point as you will find in the entire universe. There is really no way to find any rotation. I'll take that back - you can see them flip in an NMR field.
Answer D is included in B as said above.

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