The upsilon(C double bond O) and upsilon(op)(C double bond O)(2) modes
for 4-x benzoic acids in CHCl3 and/or CCl4 solutions decrease in freq
uency as the sigma(p) values for the 4-x atoms or groups decrease in v
alue while the upsilon(OH) mode increases in frequency. Different comp
lexes are formed between the CO2H and (CO2H)(2) groups as the mole% CH
Cl3/CCl4 changes from 0 to 100.