Chlorobutanoic acid

Because inductive effects operate through cr bonds and are dependent on distance, the effect of halogen substitution decreases as the substituent moves farther from the carboxyl. Thus, 2-chlorobutanoic acid has p/butanoic acid itself. 

Theoretical predictions, based on AMI MO theory, for gas-phase elimination reactions of 3-chloropropanoic and 2-chlorobutanoic acids are consistent with experimental results four-, five-, and six-membered transition states have been discussed. ... 

The distance the electron-withdrawing group is from the carboxylic acid group is also important. For example, butanoic acid has = 1.5 x 10 4-chlorobutanoic acid has K = 3 x 10" 3-chlorobutanioic acid has K = 8.9 x 10 and 2-chlorobutanoic acid has = 1.4 x 10". This shows that the chlorine is more effective the closer it gets to the carboxylic acid group. 

Problem 16.69 Convert 2-chlorobutanoic acid into 3-chlorobutanoic acid. ... 

Chlorobutanoic acid is dehydrohalogenated to 2-butenoic acid and HCl is added. H adds to give a /3-carbocation which bonds to Cl to form the /3-chloroacid. 

Figure 7.1 shows 3-bromo-2-chlorobutanoic acid in Fischer-type, zigzag (closely related to flying wedge), sawhorse, and Newman representations. 

Graphical representation of stereoisomers of 3-bromo-2-chlorobutanoic acid... 

As the substituted electronegative atom moves farther from the site of ionization, its effect on acid strength decreases. Thus, 4-chlorobutanoic acid, CICH2CH2CH2COOH, is a weaker acid (pfCa = 4.5) than 2-chlorobutanoic acid, CH3CH2CHCICOOH (pX, = 2.9). 

Since inductive effects are not transmitted very effectively through covalent bonds, the acid-strengthening effect decreases as the distance between the electron-withdrawing group and the carboxyl group increases. Of the chlorobutanoic acids that follow, the strongest acid is 2-chlorobutanoic acid ... 

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