Bromobutane, model

Using the models you made in exercise 1 of 1-bromo and 2-bromobutane, demonstrate the result of dehydrobromination. To do so, remove the bromine and a hydrogen from an adjacent carbon insert a double bond between these two carbons. How many isomers are possible from each compound Which is the more stable in the case where two are possible ... 

Make a model of one of the enantiomers of 2-bromobutane. Make a model of the enantiomer that results from an SN2 reaction in which the bromine is replaced by an OH. Make sure you have inversion of configuration. Look at the original enantiomer and visualize the OH coming in from the rear and displacing the bromine. 

Now, using the 2-bromobutane enantiomer from exercise 1, make the models of the racemic mixture formed when the bromine is replaced by OH in an SN1 reaction. Visualize the Br leaving first and the water attacking from either side of the carbocation to form the pair of enantiomers. 

Take a break and convince yourself that the two 2-bromobutane isomers are not identical, by building ball-and-stick models using four different-colored balls to represent the four different groups bonded to the asymmetric carbon. Try to superimpose them. 

Fig. 8. Stereoview of electron density distributions (90 % of the total population) calculated from AF syntheses in a cage framework consisting of (M)-TOT molecules, a) 2-Bromobutane Heavy line observed preferred (R)-configuration of the X-ray model. Thin line calculated position of the (S)-enantiomer. b) Ethyl methyl sulfoxide The composite density results from the space-averaged contribution of (S) and (R)-enantiomers (thin and heavy lines, respectively) in the approximate ratio 1 11...

The inadequacy of the X-ray model for a straightforward evaluation of the relative contribution of the dynamic and static disorders has been emphasized in the structure analysis of TOT/(dl)-2-bromobutane. Suprisingly, the / -ratio test favored space group PS, as opposed to space group P3j21, in spite of the presence of pairs of TOT molecules shown to be identical within the limits of experimental error and symmetrically related by C2 axes. In this context it was demonstrated how static disorder could be mimicked by a magnified thermal motion of the Br atom. The Hamilton test gave opposite results with the TOT/(R)-2-butanol clathrate. 

Fig. 10. Stereoview, down the c axis, of the calculated positions for (R)- and (S)-2-bromobutane (heavy and thin line, respectively). Dashed line X-ray model (one equivalent position shown). Dotted line crystallographic twofold axis...

Fig. 5 Gas chromatograms of blank (a) and spiked (b) human urine samples containing 1-bromopropane, 2-bromopropane, and 1-bromobutane as the internal standard. Static headspace sampling was used with the following conditions Tekmar model 7000 HT headspace sampler with a 1.0 ml sample loop and platen temperature of 75 C and a valve/loop temperature of 120 C. Sample equilibrium time was 34 min. The Agilent Technologies Model 6890 gas chromatograph was equipped with an Agilent J W DB-1 (dimethylpolysHoxane) column with a 1 p,m film thickness. Initial column temperature was 45 C with a 10 min hold, then increased at a rate of 12.5°C/min to a final temperature of 170°C. A microelectron capture detector (p,-ECD) was used.

The reaction of 4-mehtoxyphenylacetic acid butyl ester reacting from 4-methoxyphenylacetic acid and n-bromobutane using triphase catalysis investigated by our previous work [8] was set as a model reaction to understand the relationship between the reaction phenomenon and the structure of the resin. 

Build a model of each of the enantiomers of 2-bromobutane (see page 153). 

NOTE TO THE STUDENT Prove to yourself that the two stereoisomers of 2-bromobutane are not identical by building ball-and-stick models to represent them and then trying to superimpose one on the other. The tutorial on page 146 tells you what other models you should build as you go through this chapter. 

How can a molecule exist as two nonsuperimposable mirror images Consider the radical bromination of butane. This reaction proceeds mainly at one of the secondary carbons to furnish 2-bromobutane. A molecular model of the starting material seems to show that either of the two hydrogens on that carbon may be replaced to give only one form of 2-bromobutane (Figure 5-3). Is this really true, however ... 

This model for the transition state is based on experimental evidence. When (f )-2-bromobutane reacts with sodium hydroxide, the substitution product is (5)-2-butanol. The reaction therefore occurs with inversion of configuration. This result indicates that the nucleophile approaches the electrophilic carbon atom from the back side—that is, from the side direcdy opposite the leaving group. The leaving group departs simultaneously from the opposite side of the substrate. 

MAKE MODELS BROMOCYCLOHEXANE (S)-2-BROMOBUTANE PART C STEREOCHEMISTRY OF E2 REACTIONS... 

Make a model of (S)-2-bromobutane, and confirm that all possible staggered conformations sighting down the C2-C3 bond are shown below. 

Phosphonium salts are successfully employed for a number of synthetical applications in organic chemistry. Of a particular note is their extensive and consolidated use as phase transfer catalysts (PTC). However, the development of new compounds and applications is always under investigation. For example, an innovative quaternary phosphonium salt (QPS)-type triphase catalyst (TPC) prepared by functionalisation of cross-linked polystyrene microspheres (CPS), was recently proposed as an efficient catalyst for the model reaction of phthalimide with 1-bromobutane in a biphase aqueous/organic phase. ... 

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