Structure of alkenes

Draw the structures of alkenes that would yield the following alcohols on hydration (red - O). Tell in each case whether you would use hydroboration/ oxidation or oxymercuration. 

Show the structures of alkenes that give the following products on oxidative cleavage with KMn04 in acidic solution ... 

Maurel and Tellier showed that the variation in the structure of alkenes has a much smaller effect on the individual rates than on the competitive rates of hydrogenation on Pt/Si02 (refs. 4,5). For a group of 24 compounds, the individual rate constants, k differ by less than 10 whereas the competi-... 

Re-examination of the benzene-sensitized isomerization of alkenes revealed that the photostationary EjZ ratio critically depends on the structure of alkenes and the triplet energy of sensitizers [69]. For instance, thermal E-Z equilibrations of 2-octene 19c and 3,4-dimethyl-2-pentene 20 give the thermodynamic EjZ ratios of 3.3 and 3.5, respectively, while the photostationary E Z ratios upon benzene sensitization are 1.1 and 1.6, respectively (Schs. 9 and 10). For practical runs, the use of /7-xylene or phenol, rather than benzene, in ether is recommended, as the yellowing of the irradiated solution, which retards the photoreaction, is substantially decreased. 

The less important double bonds to nitrogen (imines) are very similar but now there is only one lone pair on nitrogen and a second G bond to whatever substituent is on the nitrogen atom. Looking down on the planar structures of alkenes, imines, and ketones we see only the ends of the p orbitals but the rest of the structures are clearly related. 

Rate-controlling C-protonation is dominant for many of the enamines over most or all of the pH range surveyed. As a class, simple enamines are among the most reactive of all alkenes toward electrophiles. We can estimate (following Tidwell and coworkers103) that the kH+ values for 1-pyrrolidinoethene and 1-phenyl-1-pyrrolidinoethene are greater than 108 M 1 s 1. That is, simple enamines are protonated on carbon faster than all the common classes of nucleophilic olefins except for the simple enolates (see Tables 4 and 6). However, the carbon basicity of enamines, in both the thermodynamic and kinetic senses, is quite sensitive to aspects of amine moiety structure, of alkene moiety structure, and of interactions (both electronic and steric) between the two. 

The oxidation on a laboratory scale can be carried out easily in a way similar to the hydrogenation of alkenes under atmospheric pressure of hydrogen using palladium black as a catalyst, tead of palladium black and hydrogen, the oxidation is carried out with PdCh and a copper salt under an oxygen atmosphere at room temperature using a similar tq>paratus. However, rates and yields of the oxidation are heavily dependent on the structure of alkenes. Also, the proper selection of solvents and reoxidants is crucial this is surveyed in the following sections. 

The chemical properties of alkanes will be compared with those of alkenes after discussing the structures of alkenes. 

Structure of Alkene Mode o f Addition Structure of Diol... 

To understand the kind of isomerism that gives rise to two 2-butenes, we must examine more closely the structure of alkenes and the nature of the carbon-carbon double bond. Ethylene is a flat molecule. We have seen that this flatness is a result of the geometric arrangement of the bonding orbitals, and in particular the overlap that gives rise to the tt orbital. For the same reasons, a portion of any alkene must also be flat, the two doubly-bonded carbons and the four atoms attached to them lying in the same plane. 

Figure 10.7 Rotameric forms of PNA and the structures of alkenic isosteres.

HRu3(CO)n)] 174 are employed in the hydrosilylation of alkenes. The selectivity of the reaction depends on the reaction conditions as well as the structure of alkenes, hydrosilanes and catalysts. For the rationale of the competitive occurrence of dehydrogenative silylation and hydrosilylation, reasonable mechanisms have been proposed... 

Going from a phosphaalkene to a phosphaalkyne, we increase the. r-contribution in the carbon phosphorus multiple bond, and would therefore expect a further down-field shift of the phosphorus resonance. However, a glance at the situation in carbon carbon multiple bond systems in particular, alkenes and alkynes, tells us that C-NMR spectra of these molecules show the carbon resonance of alkynes upheld from that of alkenes. This is usually explained by anisotropic effects associated with the linear rod-shaped structure of alkynes versus the bend structure of alkenes. As the geometries of phosphaalkenes andphosphaalkynes are analogous to alkenes and alkynes, respectively, we can assume that the explanation given for the appearance of the carbon resonance in alkynes upheld from that for alkenes in C-NMR spectra is also applicable for the respective unsaturated phosphoms compounds. 

Describe how the molecular structures of alkenes and alkynes differ from the structure of alkanes. 

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