Convert (r)-2-butonal to (s)-s-butonal

[bjon-07]

Please Help!

How do I convert (r)-2-butonal to (s)-s-butonal using toluenesulfonyl chloride tosyl chloride (tsCL) as a replacment leaving group sense -OH is such a poor leaving group.

I can normal preform this kind of reaction, if the nuclelophil is different than the orginal leaving group. I got to the point where i have (R)-2-butyl tosylate.

The leaving is TsO- I want to convert this into HO-. How should I do this? Should I add an protic acid, or Na OH.


BTW why do SN2 reaction invert the configuration. I am having a hard time visualling why they invert configuration.

 

[chem_tr]

See Walden's inversion in your textbook, this is the solution. SN₂ types of reactions involve configuration change, since first ion hits the center of the second, and configuration changes. We usually give the example of upside-down umbrella to better realize in your minds. An umbrella goes upside down when a strong wind appears. SN₂ reactions are similar to this analogy.

$$Tos-Cl + R-OH \longrightarrow Tos-OH + R-Cl$$
$$R-Cl + NaOH \xrightarrow{heat, phase~transfer~catalyst} R-OH + NaCl$$

 

[ravenprp]

To convert (r)-2-butonal to (s)-s-butonal, you can use a substitution reaction with toluenesulfonyl chloride (TsCl) as a replacement leaving group. This will convert the -OH group into a better leaving group, allowing the substitution reaction to occur.

To perform this reaction, you will need to first convert (r)-2-butonal into (r)-2-butyl tosylate, which you have already done. Then, to convert the tosylate group into the -OH group, you can use a basic hydrolysis reaction. This can be achieved by adding a strong base, such as sodium hydroxide (NaOH), to the reaction mixture. The base will deprotonate the tosylate group, forming the -OH group and toluenesulfonate (TsO-) as a byproduct.

The reason why SN2 reactions result in inversion of configuration is due to the mechanism of the reaction. In an SN2 reaction, the nucleophile attacks the carbon atom from the opposite side of the leaving group, causing the configuration to invert. This can be better visualized by looking at the transition state of the reaction, where the nucleophile and the leaving group are in a "back-to-back" arrangement. As a result, the nucleophile attacks the carbon atom from the opposite side, leading to inversion of configuration.