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Organic Chemistry

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5 out of 7

What is the name of Compound X?

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A (S)-1-bromo-1-fluoromethane
B (R)-1-bromo-1-fluoromethane
C (S)-1-bromo-1-fluoroethane
D (R)-1-bromo-1-fluoroethane
Ans. D The given structure is an ethane derivative, not a methane derivative. This rules out Choices A and B. In the Fischer projection, the horizontal lines represent the bonds extending out of the plane of the paper toward you. The vertical lines represent the bonds pointing into the plane of the paper (away from you). With this in mind, we can start the switching of groups as follows:

image\Solutions ch 19, Q 5.png

The switching is done so that the lowest ranking substituent (here, it is H) points away (into the plane of paper). The numbering or priority is based on decreasing atomic number. That means the substituent atom with the highest atomic number gets number 1, the next highest gets number 2, and so on. Since the order is clockwise, the configuration is R.