Advices For Studying Organic Chemistry

2.4A DIPOLE MOMENTS IN ALKENES

1. Cis-trans alkenes have different physical properties: m.p., b.p., solubility, and etc.
   
   
   1. Cis-isomer usually has larger dipole moment and hence higher boiling point.
   
   
   
   

Table 2.2 Physical Properties of Some Cis-Trans Isomers

Compound Melting Point (°C) Boiling Point (°C) Dipole Moment (D)

Cis-1,2-Dichloroethene -80 60 1.90

Trans-1,2-Dichloroethene -50 48 0

Cis-1,2-Dibromoethene -53 112.5 1.35

Trans-1,2-Dibromoethene -6 108 0

2.5 FUNCTIONAL GROUPS

2.5A ALKYL GROUPS AND THE SYMBOL R

Alkane Alkyl group Abbreviation

CH 4

Methane

CH 3 –

Methyl group Me–

CH 3 CH 3

Ethane

CH 3 CH 2 – or C 2 H 5 –

Ethyl group Et–

CH 3 CH 2 CH 3

Propane

CH 3 CH 2 CH 2 –

Propyl group Pr–

CH 3 CH 2 CH 3

Propane CH^3 CHCH^3

or CH 3 CH

CH 3

Isopropyl group

i-Pr–

All of these alkyl groups can be designated by R.