Predictions major elimination product

When 1-bromo-l-methylcyclohexane is heated in ethanol for an extended period of time, three products result one ether and two alkenes. Predict the products of this reaction, and propose a mechanism for their formation. Predict which of the two alkenes is the major elimination product. 

Predict the elimination products of the following reactions. When two alkenes are possible, predict which one will be the major product. Explain your answers, showing the degree of substitution of each double bond in the products. 

Predict the elimination products of the following reactions, and label the major products. 

Use Zaitsev s rule to predict major and minor elimination products. 

Predict the /3-elimination product(s) formed when each bromoalkane is treated with sodium ethoxide in ethanol (if two might be formed, predict which is the major product) ... 

Predict whether each /3-elimination reaction proceeds predominantly by an El or E2 mechanism, and write a structural formula for the major organic product ... 

Predict whether each reaction proceeds predominantly by substitution (S l or S j2) or elimination (El or E2) or whether the two compete, and write structural formulas for the major organic product(s) ... 

Chapters 11 and 12 discuss reactions of alkyl halides to give either substitution or elimination products. It is clear from Chapter 12 that elimination occurs when the nucleophile is also a strong base and when substitution is inhibited due to steric hindrance. There are many cases in which substitution and elimination compete, particularly when the substrate is a secondary alkyl halide. The solvent plays an important role in these reactions, and solvent identification is a key parameter for distinguishing bimolecular versus unimolecu-lar (ionization) processes. The nature of the alkyl halide (1°, 2°, or 3°) is important, as is the strength of the nucleophile and whether or not that nucleophile can also react a strong base. This chapter will discuss those factors that influence both substitution and elimination, as well as introduce several assumptions that will help make predictions as to the major product. 

It is difficult to predict the ratio of substitution to elimination products for first-order reactions of haloalkanes. For the majority of cases, however, 8, 1 predominates over El when weak bases are used. 

When more than one elimination product is possible, can we reliably predict which will be the major product Usually, the major product of an elimination reaction is the one that is most stable. But what can we say about the relative stabilities of alkenes In the diagram below, alkenes are ranked in order of increasing stability ... 

Chlorination. Electrophilic chlorination of quinoline (66) in neutral medium showed a positional selectivity order of 3 > 6 > 8. The 5- and 8-positions should be sterically hindered to some extent. Hammett cr+ values predict an order for electrophilic substitution of 5 > 8 = 6 > 3. Treatment with chlorine at 160-190°C converted quinoline into a mixture of 3-chloro-, 3,4-dichloro-, 3,4,6- and 3,4,8-trichloro-, 3,4,6,8-tetrachloro-, and 3,4,6,7,8-pentachloro-quinolines. At lower temperatures ( 100°C) the major product was 3-chloroquinoline, albeit in low yield. The 4-substituted species may have arisen from an addition-elimination or radical process (70JHC171). 

No medical or therapeutic procedure comes without some risk to the patient. All possible steps are taken to ensure safely, quahty and efficacy of vaccines and immunological products (Chapter 15). The risks associated with immunization procedures must be constantly reviewed and balanced against the risks of, and associated with, contracting the disease, hi this respect, smallpox vaccination in the UK was abandoned in the mid 1970s as the risks associated with vaccination then exceeded the predicted number of deaths that would follow importation of the disease. Shortly after this, in 1980, The World Health Assembly pronounced the world to be free of smallpox. Similarly, the incidence of paralytic poliomyelitis in the USA and UK in 1996 was low but the majority of cases related to vaccine use. As the worldwide elimination of poliomyelitis approaches, there is much debate as to the value of the vaccine outside of an endemic area. 

Nitrosamine formation is not the only conceivable fragmentation mechanism for compounds of structure I. By analogy to the nitrosative dealkylation reactions discussed above, one might predict that such compounds could also undergo cis elimination of nitroxyl in amide-forming reactions. Such a transformation has possibly been observed (14). During an attempt to synthesize the nitrosamino aldehyde VIII from immonium ion IX, Hecht coworkers were able to isolate only 5-10% of the desired product. The major product proved to be N-methyl-2-pyrrolidone, as shown in Fig. 10. We interpret this as evidence that an intermediate such as li can fragment not only by the Fig. 1... 

The first step is to convert the Fischer projection formulae into sawhorse projections. Note that for a base-induced elimination reaction of the E2 type, the tosyl group must be antiperiplanar to the proton or deutron being abstracted from the neighbouring carbon atom. As a consequence of this reaction mechanism, the configuration of the resulting double bond can be predicted. Because of the higher steric hindrance in the transition states leading to the Z isomers, in both cases the E isomer should be expected as the major product. 

As can be seen in Figure 9.5, neomenthyl chloride has two hydrogens in an anti-periplanar geometry with the chlorine. Either of these hydrogens can be lost in the elimination reaction, resulting in the formation of two alkenes. (All of the examples presented up to this point were chosen so that only one alkene could be formed.) Let s now address this issue of the direction of the elimination and learn how to predict which will be the major product when more than one alkene can be formed. 

Predicting the Major Products of Substitution and Elimination Reactions... 

Predict the products of SnI, Sn2, El, and E2 reactions, including stereochemistry. Use Zaitsev s rule to predict the major and minor products of eliminations. 

Predict the products of El elimination of the following compounds. Label the major products. 

Q Illustrate the uses and mechanisms of the Hofmann and Cope eliminations, and predict the major products. 

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