The structure of self-assembled monolayers of thiophenols (I), benzyl mercaptans (II), biphenylthiols (III), and 4-biphenylmethanethiols (IV) on the surface of Au(111) are compared using cyclic voltammetry, reflection absorption infrared spectroscopy, scanning tunneling microscopy, ellipsometry and contact angle measurement. The results suggest that benyzyl mercaptans and 4-biphenylmethanethiols form closely packed and ordered monolayer, irrespective of the length of a p-alkoxy substituent. For thiophenol and biphenylthiol, a film of lower surface coverage was formed. A long p-alkoxy chain (n-C16H33O) increases the intermolecular interaction and leads to a closer packing within the monolayer film. The difference is attributed to the interplay between intermolecular interaction and the bond angle preference at the thiolate head group.