[yqu2]

My professor asked us a really interesting question today.  We are covering reaction of alcohol.  basically to convert alcohol into alkyl halide, a special way of doing it (instead of just adding HX and heat) is to use PX3 (phosphate trihalide).  The alcohol is converted into alkyl halide in a SN2 manner.  On the other hand in dehydration of alcohol can be aided by POCl3, or phosphrous oxychloride.  This reaction occur in a E2 manner (the product is an alkene)  So here's his question; What makes these two similar compounds act in such a differe manner?  I have no clue.  If anyone has the Bruice book, I'm talking about the topics in pg 449 and pg 442.  Thanks

[lemonoman]

First...what makes you think PCl₃ and POCl₃ are 'similar'?



When it comes to formula...yes...but then again, CH₄ and CH₃OH are 'similar' like that.  But a quick check of their properties shows that the two have different stabilities, reactivities, and applications.

Your prof probably wants you to look at the STRUCTURE of each, and see what one has, that the other doesnt....and how that unique feature aids in each of the reactions you described.

Good luck.

[Mitch]

Lone pairs of electrons make good electrophiles, a key step in any SN2 reaction.