Dichloropentanes

One of the most striking differences between conjugated dienes and typical alkenes is in their electrophilic addition reactions. To review briefly, the addition of an electrophile to a carbon-carbon double bond is a general reaction of alkenes (Section 6.7). Markovnikov regiochemistry is found because the more stable carbo-cation is formed as an intermediate. Thus, addition of HC1 to 2-methylpropene yields 2-chloro-2-methylpropane rather than l-chloro-2-methylpropane, and addition of 2 mol equiv of HC1 to the nonconjugated diene 1,4-pentadiene yields 2,4-dichloropentane. 

Indicate which of the following molecules are optical isomers and identify the chiral carbon atoms in those that are (a) CH,CHBrCH2CH3 (b) CH3CH2CHCl2 (c) l-bromo-2-chloropropane (d) 1,2-dichloropentane. 

We have chosen the PVC diad and triad compounds 2,4-dichloropentane (DCP) and 2,4,6-trichloroheptane(TCH) as subjects for our attempt to obtain quantitative kinetic data characterizing their (n-Bu)3SnH reduction in the hope that they will serve as useful models tor the reduction of PVC to E-V copolymers. Unlike the polymers (PVC and E-V), DCP and TCH are low molecular weight liquids whose high resolution 13C NMR spectra can be recorded from their concentrated solutions in a matter of minutes. Thus, it is possible to monitor their (n-Bu)3SnH reduction directly in the NMR tube and follow the kinetics of their dechlorination. 

Yet another type of canal structure has been reported for the urea inclusion compound of 1,4-dichlorobutane 51). Even though the canals are pseudo-hexagonal in dimension, there is a significant difference in their symmetry. The host lattice is orthorhombic, space group Pbcn. The difference lies in the directions of the six pseudo-3j helices of host molecules around the walls of each canal the sequence is cyc/o-RRRLLL, as opposed to cyc/o-RRRRRR in the hexagonal inclusion compounds and cvc/o-RLRLRL in the rhombohedral. This orthorhombic host structure probably occurs also in the urea inclusion compounds with 1,5-dichloropentane and 1,6-dibromohexane 51). 

Both of the 2,3-dichloropentane diastereomers are chiral => each exhibits optical activity. 

Abstraction of a hydrogen atom from C3 of ( )-2-chloropentane produces a radical that is chiral (it contains a stereocenter at C2). This chiral radical can then react with chlorine at one face [path (a)] to produce (2lS,3.S)-2,3-dichloropentane and at the other face [path (b)] to yield (2 S, 3i )-2,3-dichloropentane. These two compounds are diastereomers, and they are not produced in equal amounts. Each product is chiral, and each alone would be optically active. 

By treatment with phosphorus pentachloride, AT-benzoylpiperidine is decomposed into benzonitrile and 1 5-dichloropentane. 

A small quantity of 2,4-dichloropentan-3-one (5%) is obtained with the a-monochloropentanone 2 during the distillation. The NMR 8uialysis for 2-chloropentan-3-one 2 is described by Wyman and Kaufman. ... 

Problem 6.53 Outline the steps needed for the following syntheses in reasonable yield. Inorganic reagents and solvents may also be used, (a) IXhloropentane to 1,2-dichloropentane. (b) IXhloropentane to 2-chloro-pentane. (c) IXhloropentane to 1-bromopentane. (d) l-Bromobutane to 1.2-dihydroxybutane. (e) Isobutyl chloride to... 

The synthesis and stmctnral characterization of a series of spirocyclic organozincates containing two five- or six-membered metallacycles in which zinc is the central spiro atom, is shown in Scheme 1. Compound 8a was prepared via an elegant one-pot synthesis, starting from 1,5-dichloropentane, ZnCl2 and a lithium/sodinm alloy (1% sodinm) in diethyl ether as a solvent (eqnation 4 in Scheme 1). Snbseqnent treatment of a soln-tion of 8a with TMEDA afforded the corresponding TMEDA complex 8b of which the structnre in the solid state was unambiguously established by an X-ray crystal structnre determination. 

Lim and Kolinsky (203) estimated the chain-transfer coefficients of 2,4-dichloropentane and 2,4,6-trichloroheptane (dimer and trimer of vinyl chloride, plus H and CH3 end-groups) as 5 x 10 4 for both compounds at 50° C, though a higher value would be expected for the latter, which has one more —CH2 CHCl-group, than for the former they suggest that this value is appropriate for Ctp for vinyl chloride polymerization. However, the poly-... 

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