Draw the cis and trans structures of hex-2-ene. Which isomer will have higher b.p. and why?
Solution and Explanation
Hex-2-ene is represented as:
\(CH_3−CH=CH−CH_2−CH_2−CH_3\)
Geometrical isomers of hex-2-ene are:
The dipole moment of cis-compound is a sum of the dipole moments of \(C-CH_3\) and \(C-CH_2CH_2CH_3\) bonds acting in the same direction.
The dipole moment of trans-compound is the resultant of the dipole moments of \(C-CH_3\) and \(C-CH_2CH_2CH_3\) bonds acting in opposite directions.
Hence, cis-isomer is more polar than trans-isomer. The higher the polarity, the greater is the intermolecular dipole-dipole interaction and the higher will be the boiling point. Hence, cis-isomer will have a higher boiling point than trans-isomer
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Concepts Used:
Alkenes
Alkenes
In organic chemistry, an alkene is a hydrocarbon containing a carbon-carbon double bond.[1]
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.
Read More: Ozonolysis
IUPAC Nomenclature of Alkenes
- An alkene or cycloalkene is indicated by the suffix (ending) ene.
- For the root name, the longest chain must include both carbon atoms of the double bond.
- The root chain must be numbered beginning at the end closest to a double bond carbon atom. If the double bond is in the chain's centre, the nearest substituent rule is used to determine where the numbering begins.
- If the compound contains more than one double bond, it is named with a diene, triene, or equivalent prefix indicating the number of double bonds, and each double bond is assigned a locator number.
Read More: Unsaturated Hydrocarbon