Boiling Points of Alkanes Branched alkanes have less surface area contact, so weaker intermolecular forces. 400 300 CH3-(CH2)n一CH3 200 n-alkanes 100 CH3 0 CH-(CH2),CH3 -100 isoalkanes CH3 -200 5 10 15 20 number of carbon atoms Copyright2005 Pearson Prentice Hall,Inc
Chapter 3 16 Boiling Points of Alkanes Branched alkanes have less surface area contact, so weaker intermolecular forces. =>
Melting Points of Alkanes Branched alkanes pack more efficiently into a crystalline structure,so have higher m.p. 50 0 even numbers uod -50 Sunjaw -100 odd numbers -150 => -200 0 5 10 15 20 number of carbon atoms Chapter 3 17
Chapter 3 17 Melting Points of Alkanes Branched alkanes pack more efficiently into a crystalline structure, so have higher m.p. =>
Branched Alkanes Lower b.p.with increased branching Higher m.p.with increased branching ·Examples: CH3 CH3-C-CH2-CH3 CH3 CH-CH2-CH2-CH3 CH3-- H-CH CH3 CH3 CH3 CH3 bp60°C bp58°C bp50°c mp-154°C mp-135°C mp-98°C => Chapter 3 18
Chapter 3 18 Branched Alkanes • Lower b.p. with increased branching • Higher m.p. with increased branching • Examples: H CH3 CH CH3 CH2 CH2 CH3 bp 60°C mp -154°C CH3 CH CH3 CH CH3 CH3 bp 58°C mp -135°C => bp 50°C mp -98°C CH3 C C 3 CH3 CH2 CH3