1-chloropropane, conformation

Additionally, it was found that the energy difference between the two transition states (3 and 4) is determined mainly by the difference in the conformational energy of the a-chloro aldehyde in the two transition states i.e., the energetic preference of transition state 3 over 4 is due to a more favorable conformation of the aldehyde rather than a more favorable interaction with the attacking nucleophile. In fact, interaction between lithium hydride and 2-chloropropanal stabilizes transition state 4, which yields the minor diastereomer. 

Ab initio STO-3G calculationswere performed on the supermolecules formed by a nucleophile and a chiral substrate (2-chloropropanal or 2-methylbutanal). The nucleophile, simulated by H , is located at 1.5 A from the carbon atom, in a direction perpendicular to the carbonyl axis. Hence, to each reaction correspond two diastereoisomeric supermolecules resulting from attack on one face or the other of the 7T system. These molecules are thus models of the diastereoisomeric transition states. In Fig Ill and IV, their relative energies are plotted as a function of their conformations. The solid (dashed) lines correspond to the transition states of type 5... 

Combining the results for propanal and chloroethanal suggests that the conformational stability of 2-chloropropanal decreases in the order 13 < 12 < li This order has been confirmed by calculations.5... 

The very small yield of CH3C1 and CH2=CH2 from 3-methoxy-l-chloropropane (equation 81) was rationalized as due to a weak participation of the CHsO substituent, since a strained four-membered cyclic transition state is not a favorable conformation in neighboring group participation. 

Sighting along the C1-C2 bond off 1-chloropropane, draw Newman projections of the moat stable conformation and the least stable conformation. 

In 1977, Anh [23] used ab initio methods to evaluate the energies of all the postulated transition structures (Figures 4.2 - 4.4) for the reaction of 2-methyl-butanal and 2-chloropropanal (the former to test the Cram, Karabatsos, and Felkin models, and the latter to test the Felkin and Comforth models). The nucleophile was H , located 1.5A from the carbonyl carbon, at a 90° angle, on each face of the carbonyl. Rotation of the C1-C2 carbon-carbon bond then provided an energy trace which included structures close to all of the previously proposed conformational models. The results for both compounds clearly showed the Felkin transition states to be the lowest energy conformers for attack on either face of the carbonyl. Inclusion of a proton or lithium ion, coordinated to the oxygen, produced similar results. It therefore appeared that Felkin s notion of attack antiperiplanar to the large substituent was correct. 

When two substituents, heavier than hydrogen, take up positions as far from one another as possible, their relative conformation is called ""staggered (formerly, trans , which is confusing because of its use in geometrical isomerism). When these two groups move opposite one another, their relative conformation is called eclipsed gauche " is intermediate). These conformations are illustrated here by 1-chloropropane in 12.34) and (12.35). 

Examples of attractive nonbonded interactions can be found in certain halogen-ated hydrocarbons. In 1-chloropropane, for example, the gauche conformation is slightly preferred over the anti conformation at equilibrium. This is not solely the... 

Application of this procedure requires knowledge of the partition functions for each molecular conformer, and the energy differences between the conformers. Calculations have been reported for hydrazine, 1-chloropropane, I-bromopropane, and buta-l,3-diene. For each of these molecules, the calculation was simplified by assuming that the... 

Kato, M. Taniguchi, Y. (1990) Effect of Pressure on Conformational Equilibria of Liquid 1-Chloropropane and 1-Bromopropane,. Chem. Phys. Vol. 93 4345-4. 

Figure 6-10 Hashed-wedged line and space-filling renditions of the transition states for Sn2 reactions of hydroxide ion with (A) 1-chloropropane, (B) 1-chloro-2-methylpropane, and (C) 1-chloro-2,2-dimethylpropane. Increasing steric hindrance from a second gauche interaction reduces the rate of reaction in (B). Sn2 reactivity in (C) is eliminated almost entirely because a methyl group prevents backside attack by the nucleophile in all accessible conformations of the substrate. (See also Figures 6-8 and 6-9.)...

Chloropropane is most stable in the gauche conformation. What does this fact indicate about the interaction of chlorine and a methyl group in this compound ... 

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