The butyne, HC≡CCF(CF₃)₂, can be prepared via the dehydro-halogenation of ICH=CHCF(CF₃)₂, the olefin is produced by the ultraviolet irradiation of mixtures of (CF₃)₂CFI and acetylene. Group IV perfluoroalkynyl derivatives (CH₃)[subscript n]M(C≡CR[subscript f])[subscript 4-n] (n = 0 ↦ 3; M = Si, Ge, Sn; R[subscript f] = CF₃> C₂F₅, CF(CF₃)₂) can be prepared by the reaction of XMg C≡CR[subscript f] (X = Br, I) with the appropriate group IV organohalide. Some, but not all, of the combinations of n, M, and R[subscript f] are described. The reaction of CH₃Si[symbol omitted]₃ with IMgC≡CCF₃ produces (CH₃)₂Si(C≡CCF₃)₂. Difluorocarbene from (CH₃)₃SnCF₃ at 150° adds to the C≡C bond of HC≡CR[subscript f] (R[subscript f] = CF₃, C₂F₅, CF(CF₃)₂) and some of the (CH₃)[subscript n]M(C≡CR[subscript f])[subscript 4-n] derivatives to give the corresponding cyclopropenes, [formula omitted] and [formula omitted] respectively. The spectral properties of the group IV perfluoroalkynyl and cyclopropenyl derivatives exhibit several novel trends. The difluorocarbene species from (CH₃)₃SnCF₃ is electrophilic and is in a singlet state in gas phase addition reactions to unsaturated bonds. The carbene adds stereospecifically to both cis- and to trans-butene-2 to give the corresponding isomeric cyclopropanes. The carbene also inserts into the Sn-H bond of (CH₃)₃SnH. The ultraviolet irradiation of mixtures of (CF₃)₂CFI and (CH₃)₃SnSn(CH₃) produces (CH₃) ₃SnCF(CF₃) ₂. A similar reaction involving (CH₃)₃SnSn(CH₃)₃ and CF₂=CFI produces (CH₃)₃SnCF=CF₂. None of the derivatives, (CH₃)₃SnR[subscript f] (R[subscript f] = C₂F₅, CF(CF₃)₂, CF=CF₂) , produces a carbene upon pyrolysis. Bis(trifluoromethyl)diazomethane reacts with HC≡CCF₃ and with CF₃C≡CCF₃ at ca. 150° to give a mixture of the corresponding isopyrazole, [formula omitted], and cyclopropene, [formula omitted]. Similar reactions of the diazo compound with (CH₃)₃MC≡CCF₃ (M = Ge, Sn) produce [formula omitted] derivatives. The reaction of bis(trifluoromethyl)diazirine and (CH₃)₃GeC=CCF₃ also produces the cyclopropene. The diazo compound inserts C(CF₃)₂ into the M-H bonds of (CH₃)₃SnH and (CH₃)₂AsH and produces (CH₃ )₂AsCF(CF₃) ₂H and (CH₃)₂AsCF=CF₂ upon reaction with (CH₃)₂AsAs(CH₃)₂. The diazo compound fails to react however, with either (CH₃)₃MH (M = Si, Ge), (CH₃)₃GeBr, or (CH₃)₃ GeGe(CH₃ )₃. The Mössbauer spectra of the compounds (CH₃)₃SnR[subscript f] reveal that the quadrupole splitting in the Sn nucleus increases in the order R[subscript f] = CFH₂ < CF₂H < CF₃ ≲ CH(CF₃)₂ < C₂F₅ < CF(CF₃)₂ which indicates the order of increasing electronegativity of the R[subscript f] groups. The order of electronegativity, CF₃ < C₂F₃ < CF(CF₃)₂, is also supported by n.m.r. studies of the compounds HC≡CR[subscript f] and [formula omitted]. As an Appendix the stereochemistry of the olefins produced by the ultraviolet irradiation of mixtures of R[subscript f]I (R[subscript f] = CF₃, C₂F₅, CF(CF₃)₂) and acetylene is described. Predominantly trans addition takes place. / Science, Faculty of / Chemistry, Department of / Graduate