Highly correlated ab initio calculations with large basis sets are reported for formyl fluoride, OCHF; difluorocarbene, CF2; monofluoromethylene, CHF, and difluoromethane, CH2F2. Based on CCSD(T)/cc-pVQZ results (including a correction for the effect of diffuse functions on fluorine and oxygen), equilibrium structures are derived. These structures are compared to experimental results, when available, and to those of similar molecules; and their accuracy is discussed.