Problems (References for these problems will be found on page 797), 1. Predict t

Question

Problems (References for these problems will be found on page 797), 1. Predict the order of increasing thermodynamic acidity in each series of compounds: L (a) benzene, 1,4-cyclohexadiene, cyclopentadiene, cyclohexane (b) CH,CN, CH,NO, CHCH,CHSCH,CHSCH (C) PhCH3, PhCH2Si(CH3)3-PhSCH3, PhCH2SCH3 (e) 9-(m-chlorophenyl)fluorene, 9-(p-methoxyphenyl)fuorene, 9-phenyifuorene 9-(m-methoxyphenyl)fluorene, 9-(p-methylphenyl)fuorene. 2. Indicate which portion is the most acidic in each of the following molecules. Explair your reasoning. 0

Explanation / Answer

a. cyclohexane,< benzene, <1,4 cyclohexadiene,< cyclopentadiene

this is based on more s character in bonding more acidity sp2 benzene greater than sp3 cyclohexane

cyclopentadiene on losing the proton attains aromaticity more acidic compared with 1,4 cyclohexadiene which increases delocalisation on losing a proton

b. CH3NO2>CH3SO2CH3 >CH3SOCH3> CH3CN> CH3COCH3

BASED ON NEGATIVE INDUCTIVITY OF FUNCTIONAL GROUPS

C PHSO2CH3 >PhCH2SO2CH3 >PhCH3 >PhCH2Si(CH3)3

based on electron withdrawing group Ph and SO2 its relative position

d PhCOCH2COCF3> PhCOCH2COCH3>CH3COCH2COCH3>CH3CH2COCH2COCH2CH3

ACIDITY INCREASES WITH PI ACCEPTORS PRESENCE

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