Organic Chemistry

Organic Chemistry - Ch 11 553 Daley & DaleyHCHOC OHCH 2 OHHCHOOHCH 2 OHRotateo180HOCH 2 OHCHOHHOCH 2 OHC HCHOHowever, rotating the projection by 90 o is NOT allowed, as it changesthe configuration of the projection. A 90 o rotation no longer fits theconvention of horizontal lines forward and vertical lines backward. A90 o rotation reverses this convention.HCHOC OHCH 2 OHHCHOOHCH 2 OHRotate90oHOH 2 CHOHCHO/HOH 2 CHCOHCHOYou may not turn the figure over, because this also gives an incorrectrepresentation of the structure.CHOCHOCHOCHOHCOHHOHFlip HO H /HOCHCH 2 OHCH 2 OHCH 2 OHCH 2 OHBoth the 90o rotation and flip operations drawn above actually aredrawing the enantiomers of the initial structures.When drawing a longer chain with the stereocenter in themiddle of a chain, the convention is to arrange the chain verticallywith the longer part of the chain at the bottom of the structure.CH 3CH 3HHC OH H OHCH 2 CH 3 CH 2 CH 3NotCH 3OHCH 2 CH 3Solved Exercise 11.2Consider the following pairs of Fischer projections. What operation was doneto go from one projection to another: flip or rotate 90 o , 180 o , or 270 o . Are thetwo structures the same molecule or are they enantiomers?a)www.ochem4free.com 5 July 2005