The generic structural formula for a 1-alkyl-3-methylimidazolium cation is

Where R is a ¬CH2(CH2)nCH3 alkyl group. The melting points of the salts that form between the 1-alkyl-3-methylimidazolium cation and the PF6- anion are as follows:
R = CH2CH3 (m.p. 60 °C), R CH2CH2CH3 (m.p. 40 °C),
R= CH2CH2CH2CH3 (m.p. 10 °C) and
R = CH2CH2CH2CH2CH2CH3(m.p. = - 61 oC). Why does the melting point decrease as the length of alkyl group increases?

Transcribed Image Text:

Н НаС 'N -R Н Н