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

1. Nov 16, 2004

### bjon-07

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.

2. Nov 17, 2004

### 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.

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