Stercochemistry Workshop Problems-2, fall3017 1. The complete IUPAC name for the

Question

Stercochemistry Workshop Problems-2, fall3017 1. The complete IUPAC name for the following compound is CHICH A) S1-uro-2-methylbutane C) (S-2-1-uro-2-methylbutane 2. The complete IUPAC name for the following composnd is B) (R 1-fturo-2 methylbutaee A) (S)-bromochlorotluromethane B) (R) bromochloroftharomethane 3. Following are the four stereoisomers of 3-amim0-2-butano - CHy CH, CH CH, OH OH CH IDI (a) Using the (R.S) notation provide complete stereochemical names for each of these sterevisomers Answer A] [cj (b) Stereoisomer [C] is a crystalline solid, stereoisomer [A ] is a liquid. Which other stereoisomer would you expect to be a crystalline solid? Explaiz

Explanation / Answer

Q1.

Rules for S/R configuration.

First, identify the CHIRAL center, recall that the chiral center must be bonded to 4 different types of "branches" that is, they should NOT repeat each other, such as CH3, CH3.. It should have all 4 substituents completely different.

Second, Classify by "importance", recall that we must number from high to low atomic number sizes. For Chorine, Cl , Z = 35, which is larger than Carbon with Z = 12. Note that by definition, Hydrogen has Z = 1, so this is the least important specie. Then, Cl > C > H is a good example.

Third, Number 1,2,3,4 in the chiral center

Fourth, Write a line in the 1,2,3 flow...

Fifth, If the least important specie is bonded to the BACK (i.e it has dashed bond lines) then, follow this:

If counterclockwise rotation = S notation

If clockwise rotation = R notation

Sixth , If the least important specie is bonded to the FRONT (i.e it has bold/wedge bond ) then, follow this:

If counterclockwise rotation = R notation

If clockwise rotation = S notation

Then

order of groups:

CH2F > CH2CH3 > CH3 > H

number goes --> clockwise

then

"R" configuration

then...

1-fluoro

2-methyl

total carbons --> 1+1+2 = 4 , therefore butane

the best option is

(R) -1-fluoro-2-methylbutane

Q2.

similarly,

number of imporntance

Br > Cl > F > H

then, this appears to be: "S" since it is counterclockwise

but Br is "dashed " line, then S must conver tto R

then,

Carbon 1 --> bromo, chloro, fluoo ( in ABC order)

choose B

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