Acetylene, HCCH

Vibrational Eigenfunctions Using a Modified Single Lanczos Method Application to Acetylene (HCCH). 

Quantum Calculations of Vibrational Energy Levels of Acetylene (HCCH) up to 13000 cm-1. 

A similar reaction of vinylcyanide H2C2HCN with HCCH yields HC5N. In this context the reaction of acetylene, HCCH, with fuiminic acid, HCNO, is of interest, since it produces HCCCN but not HCC-CNO (Winnewisser et al. 1981) ... 

Normally, a 10-valence electron system such as acetylene, HCCH, possesses a linear structure, which can be rationalized by the shape of its bonding a-MOs, namely the C,C bonding (2a,) MO and the two C,H bonding MOs (2a and 3bonding overlap of 2pa(C) orbitals, which means that bending of acetylene leads to a decrease of C,H bonding and, hence, to an increase of the molecular energy. 

Typical electron momentum densities with (3, — 1) and (3, +1) saddle points at zero momentum are found in MgO and acetylene (HCCH), respectively. A momentum density with a zero momentum (3, — 1) critical point is shown for MgO in Fig. 19.6. In the vertical plane of symmetry /T(p, 0,pj has the structure of two hills separated by a ridge or col, and one sees two local (and global) maxima located symmetrically along the p axis. The plot in the horizontal symmetry plane has the structure of a hill. 

Interesting reactions of lb are additions to acetylene HCCH and difluoroa-eetylene FCCF. The reaction with HCCH directly leads to the methylenecyclo-propene 13a, and no other intermediates are observed. [43] In contrast, the reaction with FCCF yields allenylcarbene 14b as the primary thermal product. Visible light irradiation is required to induce the rearrangement to the corresponding methylenecyclopropene 13b. This clearly demonstrates that the formation of the methylenecyclopropene is a two-step reaction with carbene 14b as an intermediate. 

Optimized geometries computed at MC-SCF/STO-3G and MC-SCF/4-31G for fulminic acid (HCNO) and acetylene (HCCH) (atoms labelled as in Fig. 37). 

Such hybridization is said to occur in acetylene HCCH, which after optimization of the FTartree-Fock energy, corresponds to the linear symmetric configuration. According to this explanation, each carbon atom exposes two hybrids (Fig. 8.27c) one towards its carbon and one towards its hydrogen partner. These hybrids use... 

In 1,2-propadiene (allene, CH2=C=CH2) the carbon-carbon double bonds are shorter (131pm) than those in isolated alkenes (134pm in ethene [ethylene, CH2=CH2]) but longer than in alkynes (120pm in ethyne [acetylene, HCCH]). 1,2-Propadiene (allene, CH2=C=CH2) is about 6.25kJmol" (1.5kcalmol" ) less stable than propyne (methylacethylene, CHsC CH). 

In ethyne or acetylene (HCCH), shown in Rgure 1.21, two of the four bonding electrons in each carbon are used in forming single bonds to one hydrogen and the other carbon. Two electrons are left over on each carbon, and these are shared to create a triple bond between the carbons. 

Find the symmetry representations of the C — H stretching vibrations in acetylene, HCCH, and determine whether any are IR active or Raman active. 

Another example is acet (from acetylene, HCCH), which is an alternate name for a two-carbon group. 

Consider the hydrocarbon species methane (CH4, sp ), ethylene (H2CCH2, sp ), and acetylene (HCCH, sp ) as prototype examples of sp bonding, using idealized Pople-Gordon comparison geometry as shown below ... 

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