What is the difference between structural isomers and geometric isomers? What are examples of both?

1 Answer
anor277
Aug 29, 2016

Well structural isomers differ in their connectivity..........

Explanation:

And geometric isomers have identical connectivity, but differ in their geometry, their peculiar spatial arrangement.

If we take #"butene"# as an examplar, #"butene"# can generate 2 structural isomers, #"1-butene"# versus #"2-butene"#, i.e. #H_2C=CHCH-CH_3# versus #H_3C-CH=CH-CH_3#. Now, clearly the 2 isomers are structurally distinct, by reason of the position of the olefinic bond. The isomers are distinguished by their connectivity, and are hence decribed as structural isomers.

On the other hand, for #"cis-2-butylene"# versus #"trans-2-butylene"#, these geometric isomers have identical connectivity: #C1# connects to #C2# connects to #C3# connects to #C4# in EACH isomer.

chemlibretexts.org

What distinguishes the cis versus trans isomers is the disposition of the alkyl groups across the double bond. This is clearly a geometric difference that results in different physical properties, and different chemistry.

Capisce?

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