Bond distances propyne

How do the bond ) distances of molecu lar models of propene and propyne com pare with the experimental values ... 

The first step in the addition of an electrophile such as HBr to an alkyne involves protonation and subsequent formation of an intermediate vinyl cation. Where does propyne protonate Compare energies of 1-methylvinyl and 2-methylvinyl cations. Which is more stable Why Measure CC bond distance in the more stable cation. Does the cation incorporate a full triple bond (as in propyne) or a double bond (as in propene). Examine atomic charges and electrostatic potential maps to locate the positive charge in the two cations. Is the more stable ion the one in which the charge is better delocalized Use the charges together with information about the ions geometry to draw Lewis structures (or a series of Lewis structures) for 1-methylvinyl and 2-methylvinyl cations. 

One type of application involves the estimate of empirical offsets by comparing ab initio distances with experimental or rg distances and to use these offsets as constraints in fits of structural parameters for similar molecules. Le Guennec et al. [64] used two different basis sets, a double-zeta basis with a single set of polarization functions (DZP) and a triple-zeta basis with two sets of polarization functions on C and N atoms (TZ2P), at three different levels of theory (SCF, MP2 and QCISD). For each type of calculation, they derived offsets for C-H, C-C, CsC and CsN bonds with which they predicted the rg structure of propyne, HCSCCH3. Similar of ets determined for smaller basis sets (6-31G(d), 6-311G(d,p) and 6-311+G(d,p)) and electron correlation at fire MP2 level have been used for acrylonitrile [65] and a series of dicyanides [48]. 

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