Solved: Intermolecular Forces (Section)The generic

Chapter , Problem 32E

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

where \(R \text { is } a-\mathrm{CH}_{2}\left(\mathrm{CH}_{2}\right)_{n} \mathrm{CH}_{3} \) alkyl group. The melting points of the salts that form between the 1 -alkyl-3-methylimidazolium cation and the \(P F_{6}^{-}\) anion are as follows:

\(R=\mathrm{CH}_{2} \mathrm{CH}_{3}\left(m \cdot p .=60^{\circ} \mathrm{C}\right), \mathrm{R}=\mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\left(m \cdot p .=40^{\circ} \mathrm{C}\right), \mathrm{R}=\mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\left(m \cdot p .=10^{\circ} \mathrm{C}\right)\)

and  \(\mathrm{R}=\mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\left(m \cdot p .=-61^{\circ} \mathrm{C}\right)\)  Why
does the melting point decrease as the length of alkyl group increases?

Equation Transcription:

Text Transcription:

R  is  a-CH2(CH2)nCH3

PF6-

R=CH2CH3(m.p.=60°C), R=CH2CH2CH3(m.p.=40°C), R=CH2CH2CH2CH3(m.p.=10°C)

R=CH2CH2CH2CH2CH2CH3(m.p.=-61°C)