The interaction between syntax and phonology has long been an object of study, and recent work on this interface in Spanish has examined aspects of focus and intonation (Domínguez 2004, Elordieta, Gorka & Vigário 2005). Here, I identify a syntactic structure influencing different phonological processes that have not yet been approached within the syntax-phonology interface: the head-(head of) complement structure, formed by linear adjacency of a word representing the syntactic head and the word representing the head of its syntactic complement. Sensitivity to this linear syntactic relationship is expressed here in Optimality-Theoretic terms (Prince & Smolensky 1993) via positional markedness constraints (Smith 2005) targeting the head-complement structure. Three phonological processes of Spanish are examined using the head-complement positional markedness schema: morpho-phonological determiner alternation, coda-gliding, and conjunction. Using this syntactic "position" in positional markedness necessarily expands the phonological framework to a two-constituent targeted environment instead of a singleton one, and it directly links syntax and phonology by allowing phonological constraints to access this syntactic information, bypassing prosodic hierarchy. Some alternative approaches to these two proposals are evaluated, ultimately arguing in favor of the two-constituent environment and direct syntax-phonology relationship. The paper concludes with some remarks on theoretical implications and avenues of further research.