2-Bromobutane enantiomers

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. 

Would you expect two enantiomers such as (R)-2-bromobutane and (S)-2-bromobutane to have identical or different IR spectra Explain. 

Problem 7.35 Dehalogenation of Wc-dihalides with active metals (Mg or Zn) is also an anti elimination. Predict the products from (a) meso- and (b) either enantiomer of 2,3-bromobutane. ... 

Exercise 8-8 Explain how, in the presence of bromide ion, either enantiomer of 2-bromobutane racemizes (Section 5-1B) in 2-propanone solution at a rate that is first order in Breand first order in 2-bromobutane. 

Exercise 8-9 When either of the enantiomers of 1-deuterio-1-bromobutane is heated with bromide ion in 2-propanone, it undergoes an SN2 reaction that results in a slow loss of its optical activity. If radioactive bromide ion (Br e) is present in the solution, radioactive 1-deuterio-1-bromobutane is formed by the same SN2 mechanism in accord with the following equation ... 

One-step addition of H-Br to the top face of the double bond gives (S)-2-bromobutane. Addition of H-Br to the bottom face gives (fi)-2-bromobutane. Since 1-butene is achiral, the probability of addition to either face of the double bond is equal, and the product will be racemic (an equal mixture of enantiomers). 

Under certain conditions, when (R)-2-bromobutane is heated with water, the SN1 substitution proceeds twice as fast as the SN2. Calculate the e.e. and the specific rotation expected for the product. The specific rotation of (R)-butan-2-ol is —13.5°. Assume that the SN1 gives equal amounts of the two enantiomers. 

When ( )-2,3-dibromobutane reacts with potassium hydroxide, some of the products are (2S,3f )-3-bromobutan-2-ol and its enantiomer and frawx-2-bromobut-2-ene. Give mechanisms to account for these products. 

Most of (Jie biochemical reactions that take place in the body and manj organic reactions in tbe labaratory yield products chirality centers. Fw example, addition of HBr ta l cule. What predictions can we make about the stereochemistry of this rtu-rai product If a single enantianrer is formed, is it A or 5 If a noixtute oS enantiomers id formed, how much -of each In fact, the 2-bromobutane pre duerd is a racemic mixture of R and S enancioiners. Let s sec why. 

Thus, four isomers are formed by chlorination of (R)-2-bromobutane at C2 and C3. Attack at the stereogenic center (C2) gives a product with one stereogenic center, resulting in a mixture of enantiomers. Attack at C3 forms a new stereogenic center, giving a mixture of diastereomers. 

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. 

When a reactant is chiral but optically inactive because it is racemic, any products derived from its reactions with optically inactive reagents will be optically inactive. For example, 2-butanol is chiral and may be converted with hydrogen bromide to 2-bromobutane, which is also chiral. If racemic 2-butanol is used, each enantiomer will react at the same rate with the achiral reagent. Whatever happens to (7 )-( )-2-butanol is mirrored in a corresponding reaction of (5)-(-b)-2-butanol, and a racemic, optically inactive product results. 

Nonsuperimposable mirror-image molecules are called enantiomers (from the Greek enantion, which means opposite ). The two stereoisomers of 2-bromobutane are enantiomers. A molecule that has a nonsuperimposable mirror image, like an object that has a nonsuperimposable mirror image, is chiral. Each of the enantiomers is chiral. A molecule that has a superimposable mirror image, like an object that has a superimposable mirror image, is achiral. To see that the achiral moleule is superimposable on its mirror image (i.e., they are identical molecules), mentally rotate the achiral molecule clockwise. Notice that chirality is a property of the entire molecule. 

First, let s look at how you can determine the configuration of a compound drawn as a perspective formula. As an example, we will determine which of the enantiomers of 2-bromobutane has the R configuration and which has the S configuration. 

A mixture of equal amounts of two enantiomers—such as (/ )-(—)-lactic acid and (6 j-(+)-lactic acid—is called a racemic mixture or a racemate. Racemic mixtures do not rotate the plane of polarized light. They are optically inactive because for every molecule in a racemic mixture that rotates the plane of polarization in one direction, there is a mirror-image molecule that rotates the plane in the opposite direction. As a result, the light emerges from a racemic mixture with its plane of polarization unchanged. The symbol ( ) is used to specify a racemic mixture. Thus, ( )-2-bromobutane indicates a mixture of (-l-)-2-bromobutane and an equal amount of (-)-2-bromobutane. 

Whether a particular sample consists of a single enantiomer or a mixture of enantiomers can be determined by its observed specific rotation. For example, an enantiomerically pure sample—meaning only one enantiomer is present—of (5)-(+)-2-bromobutane will have an observed specific rotation of -1-23.1° because the specific rotation of (6)-(-l-)-... 

For example, if a sample of 2-bromobutane has an observed specific rotation of +9.2°, its optical purity is 0.40. In other words, it is 40% optically pure—40% of the mixture consists of an excess of a single enantiomer. 

Enantiomers can be separated easily if they are subjected to reaction conditions that cause only one of them to react. Enantiomers have the same chemical properties, so they react with achiral reagents at the same rate. Thus, hydroxide ion (an achiral reagent) reacts witli (/ )-2-bromobutane at the same rate that it reacts with... 

The reaction of 2-bromobutane with hydroxide ion forms a substitution product with an asymmetric carbon. The product, therefore, can exist as enantiomers. 

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...

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