Differentiate between alkenes and alkynes, cis isomers and trans isomers. 

Expert Answers

An illustration of the letter 'A' in a speech bubbles

The main difference of alkene and alkyne is the number bonds that they have between two carbon atoms. Alkene has a `C=C` or double bond while alkyne has `C-=C` or triple bond in the structure.

Cis and trans notation for isomer is used in alkenes in determining the   orientation of the functional groups attached in the `C=C` bond. When the substituent groups are oriented in the same direction, it is named as cis isomer. If opposite, trans isomer. 

Let me show you the difference between the cis and trans isomers of 1,2-dichloroethene. Notice the orientation of the Cl substituents.

 

Cl       Cl
  \      /
   C=C
  /      \
H        H

cis-1,2-dichloroethene

 

Cl       H
  \      /
   C=C
  /      \
H        Cl

trans-1,2-dichloroethene

 

 

Approved by eNotes Editorial Team