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Home Layout Document Elements Tables Charts SmartArt Review Paragraph Times AaBbCcDdEAa Normal Note 19. The dehydration of 2,3-dimethyl-2-butanol with phosphoric acid yields two 1lkenes: HO CH 150C C H20 0% 2,3-dimethyl-2-butancol 2,3-dimethyl-1-butene 2,3-dimethyl-2-butene MW 102.18 g/male B.P 84.16 g/male 84.16 g/mole 73 C 120 C 56 C A GC analyis of the product misture wing ais-ot, SE-30 packed column at 110 C affordod te sollowing Time (min) Area 4.45 4.88 53655 start The compound responsable orthe major pe1k (RT-4.88} was isalated and an spectroscopic analysis done: 0.9 0.6 0.45 3000 2000 1000 Wavenumber (cm-1) a)Based on the expcrimental data (G C. and IR), hich alkene is the major prodset? Defend your b)Calculate the percet composition of he compoand rexponxible for the peak at 4.RB. Axxame the responsc factoes for the two compounds are the aame3 point (c.) Give three distinct changes that could bc tude to increase the resolution ofthe two peaks in the gax Print Layout View Sec Pages: 7 of 9 Words: 709 of 1073

Explanation / Answer

19. Dehydration of 2,3-dimethyl-2-butanol

GC of product mixture is done

(a) The major product formed is 2,3-dimethyl-2-butene, the most substituted alkene. The reaction follows an E1 elimination pathway, wherein, the first step is protonation of -OH group to form more labile H2O. The H2O leaves to form a tertiary carbocation center. Loss of H to to H2O gives the most subtituted alkene product by saytzeff rule. The GC also shows that the major product has higher boiling point which is for 2,3-dimethyl-2-butene product.

(b) Percent composition

2,3-dimethyl-1-butene (4.45 ) = 2209/(2209 + 53655) = 3.96%

2,3-dimethyl-2-butene (4.88 ) = 53655/(2209 + 53655) = 96.04%

(c) We may reduce the flow rate of the mobile gas to increase the retention of the components on the column, which would improve the resolution of the peaks on the column. The column temperature could also be reduced to increase the retention times for the component which would result in better separation and greater resolution. Increasing the column length would also improve the resolution as now components can stay at the column for longer time.

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