W configuration

ACS Symposium Series American Chemical Society Washington, DC, 19S0. 

Multifunctk tK)l Diphosphonote HEDP ond HMDP (possibly others) 

---

Fig. 15. The stereoisomeric thiourea-platinum complexes shown in (a) display large 4/ptjC couplings for the a-carbon atom in that branch of the X.X-dialkyl substituent which is in a favourable W configuration with respect to the metal atom (thick bonds). The assignment of the (fortuitously overlapping) H and 195Pt NMR signals of all three stereoisomers was feasible by means of indirect detection of these couplings from a XH detected H/(13C)/195Pt correlation spectrum which is shown in (b) together with the one-dimensional and 195Pt NMR projections. Reproduced from Ref. 44 by permission of John Wiley Sons.

The same reaction in the opposite direction—the ring closure of an allyl cation—is also known. The remarkable formation of the thermodynamically less favoured cw-di-t-butylcyclopropanone 4.72 from the zwitterion 4.71, which probably has the W configuration, is evidence of its being disrotatory. 

In the aldol reaction between butanone and benzaldehyde it is important to note that butanone can form more than one enolate. Under the reaction conditions given, formation of the more substituted and thermodynamically more stable enolate will be produced, and this can be either E- or Z-configured. Moreover, nucleophilic attack at the aldehyde group of the planar benzaldehyde can take place both from the Re or Si sides. Four products are therefore obtained. From the Z enolate the /-configured enantiomers A and B are the preferred products, whilst the E enolate gives predominately the w-configured enantiomers C and D. 

According to Cram s rule, the w-configured pair of enantiomers (the 2i ,3S and 2S,3R isomers) will be the preferred products when rac-2-methylbutanal reacts with hydrogen cyanide. The byproduct will be the /-configured race-mate (2.RS,3i S)-2-hydroxy-3-methylpentanenitrile. 

Fig. 4 Gas-expansion gas-liquid separators. a modified Vijan-type U-tube separator b. Perkin-Elmer W-configuration separator and c, modified W-configuralion separator with PTFE tube scrubber. G-L, gas-liquid mixture D, to detection system W. to waste pump B. glass beads T, microporous PTFE lube with blocked end O, outer tube with gas outlet.

---