Three structural isomers with molecular formula are listed below along with measured…

CHEMISTRY · Multi-part · A Level · Chemistry · Bonding · Bonding

Problem

Three structural isomers with molecular formula

C_{4}H_{10}O

are listed below along with measured viscosities at

25\,^{\circ}\text{C}

Substance (condensed formula)	Dynamic viscosity (mPa·s)
1-Butanol ( $CH_{3}CH_{2}CH_{2}CH_{2}OH$ )	2.95
sec-Butanol ( $CH_{3}CH_{2}CH(OH)CH_{3}$ )	3.26
tert-Butanol ( $((CH_{3})_{3}C-OH)$ )	12.4

Answer the following questions. (1) Part 1: (a) Rank the three isomers in order of increasing expected surface area available for dispersion interactions. Justify your ranking. (2) Part 2: (b) Despite your answer in part (a), tert-butanol has the highest measured viscosity. Explain this apparent anomaly by discussing all relevant intermolecular forces. (3) Part 3: (c) Predict which isomer would have the lowest vapor pressure at

25\,^{\circ}\text{C}

and justify your answer. (4) Part 4: (d) The student replaces the

-OH

group in tert-butanol with

-OCH_{3}

, producing tert-butyl methyl ether. Predict qualitatively how the viscosity of the new compound will compare with that of tert-butanol and explain your reasoning.

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