Rules of the Day 2-14-07

Click here for a copy of the imine formation mechanism sheet used in lecture today.

You can see streaming video of all previous lectures this semester at http://cns.utexas.edu/lectures/classes.asp

Use login: 53760

Password: ch31on (lower case)

You will need these downloads: http://cns.utexas.edu/lectures/downloads.asp

Note the new intel based macs need a new plug-in which is now available. For more information see: http://cns.utexas.edu/lectures/

Featured "Golden rule of chemistry": 5. Most reactions involve nucleophiles (molecules with a location of particularly high electron density) attacking electrophiles (molecules with a location of particularly low electron density). When in doubt, transfer a proton!

1. Imines are formed when a primary amine or ammonia reacts with an aldehyde or ketone with some acid around. The mechanism involves mechanism C to make a aminal, followed by protonation of the OH group then loss of water at the same time a proton is lost from the nitrogen atom. Like acetal formation, this process is reversible and can be run in either direction depending on the ratio of amine (ammonia) to water in the solution.

2. Aldehydes are easily oxidized to carboxylic acids using H2CrO4 in H2O.

3. Aldehydes and ketones can be reduced by H2/Pd to give alcohols. (Watch for racemic mixtures!) Note that this method will also reduce any carbon-carbon double or triple bonds that happen to be in the molecule.

4. Metal hydride reagents can be used to reduce aldehydes and ketones to alcohols, but in this case carbon-carbon double or triple bonds are NOT reduced. In these reagents, NaBH4 (less reactive) and LiAlH4 (more reactive), the hydrogen atom is the nucleophile, that attacks a carbonyl carbon atom to give a tetrahedral intermediate, followed by addition of water to the reaction flask that protonates the oxyanion to give the alcohol product. Mechanism A.

Homework: Read: 16.10-16.12 Problems: 16.11-16.13, 16.43, 16.46, 16.51