The1H nmr spectral parameters for 2-alkylthio derivatives benzaldehyde (alkyl = CH3, CH2CH3, CH(CH3)2, C(CH3)3) are used to show that the O-synconformation of the aldehyde group decreases from 40% for the methyl to zero for thetert-butyl compound in CC14solution at about 300 K. It appears that the alkylthio groups twist out of the benzene plane to the same extent as in the alkyl phenyl sulfides and that it is the concomitant approaches of the 3plone-pairs on sulfur into the ring plane which, by repulsive interactions with the C=O bond, determine the conformations of the aldehyde group. The spectral parameters display interesting changes as the size of the alkyl group increases. For example, the chemical shift of the aldehydic proton is larger than that reported for any other benzaldehyde derivative in CCl4solution.