2- methylvinyl cation

LUMO of 1-methylvinyl cation reveals the likely site for nucleophilic attack. 

Electrostatic potential map for 2-methylvinyl cation shows most positively-charged regions (in blue) and less positively-charged reigons (in red). 

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 synthesis approach towards y-hydroxylated ionic liquids is a Michael-type addition of a protonated ammonium salt to a a, /l-an sal uni led carbonyl compound such as methylvinyl ketone yielding an oxobutyl functionalized cation. Intrinsically unstable due to retro-Michael reaction, this OS could however be transformed by a heterogeneous catalyzed hydrogenation reaction yielding a hydroxyl functionalized TSIL [24] (Fig. 7). 

Different stimuli could trigger the transition of the smart polymer making it possible to produce membranes whose permeabihties respond to these stimuh. When a copolymer of NIPAAM with triphenylmethane leucocianide was grafted to the membrane, it acquired photosensitivity—uv irradiation increases permeation through the membrane (78). Fully reversible, pH-switchable permselectivity for both cationic and anionic redox-active probe molecules was achieved by depositing composite films formed from multilayers of amine-terminated dendrimers and poly(maleic anhydride-co-methylvinyl ether) on gold-coated silicon (79). 

Liu, M., Britt, P.F. and Mays, J.W. (2004) Synthesis of amphiphihc miktoarm star copolymers A2B2 of polystyrene and poly( ethylene oxide). ACS Polym. Prepr. (Div. Polym. Chem.), 45(2), 555-556. Bae, Y.C. and Faust, R. (1998) Living coupling reaction in hving cationic polymerization. 2. Synthesis and characterization of amphiphihc A2B2 star-block copolymer PlB-star-bis (methylvinyl ether). Macromolecules, 31,2480-2487. 

In 2002, Strukul et al. [18] reported the synthesis of a series of Pd(II) and Pt(II) cationic complexes of the types [(P-P)M-(solv)](Y)2, [(P-P)M(h2-Y)](Y), and [(P-P)M(m-Cl)]2(Y)2 (P-P = various diphosphines including chiral diphosphines M = Pd, Pt Y = TfO , Cl04, Bp4 ) (Figure 16.2). The variety of cationic complexes of Pd(II) (57) and Pt(II) (58) were found to be active catalysts for the Diels-Alder reaction between cyclopentadiene or cyclohexadiene and a number of simple dienophiles such as acrolein, methacrolein, and methylvinyl ketone. Some of the complexes modified with chiral diphosphines promoted enantioselective Diels-Alder reaction with moderate enatiomeric excesses up to 49% ee. 

---