Advices For Studying Organic Chemistry

and with it the strength of the van der Waals forces operating between it and

adjacent molecules ⇒ lowering the boiling.

4.7B MELTING POINTS

1. There is an alteration as one progresses from an unbranched alkane with an even
   number of carbon atoms to the next one with an odd number of carbon atoms.

1. Melting points: ethane (–183 °C); propane (–188 °C); butane (–138 °C);
   pentane (–130 °C).

Figure 4.4 Melting points of unbranched alkanes.

2. X-ray diffraction studies have revealed that alkane chains with an even number
   of carbon atoms pack more closely in the crystalline state ⇒ attractive forces
   between individual chains are greater and melting points are higher.


3. Branching produces highly symmetric structures results in abnormally high
   melting points.

1. 2,2,3,3,-Tetramethylbutane (mp 100.7 °C); (bp 106.3 °C).

CC

CH 3 CH 3

H 3 C

CH 3 CH 3

CH 3

2,2,3,3,-Tetramethylbutane