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Example Questions
Example Question #11 : Help With Enantiomers
How many possible stereoisomers does the following steroid derivative have?
Here there are 11 asymmetric carbons and one E/Z isomerism.
So, the number of possible stereocenters from asymmetric carbons is , and the number of possible stereoisomers from E/Z isomerisms is .
Thus the number of stereoisomers from asymmetric carbons is doubled, and possible stereoisomers
Example Question #41 : Stereochemistry
What is the IUPAC name for the given organic molecule?
(3S, 5R)-2,2,3-trimethylhexan-5-ol
(3R, 5R)-2,2,3-trimethylhexan-5-ol
(2R, 4S)-4,5,5-trimethylhexan-2-ol
(2S, 4R)-4,5,5-trimethylhexan-2-ol
(2R, 4R)-4,5,5-trimethylhexan-2-ol
(2R, 4S)-4,5,5-trimethylhexan-2-ol
The absolute configuration around carbons 2 and 4 is R and S, respectively. The molecule is a hexanol, and the numbering starts with the carbon closest to the hydroxyl group.
Example Question #42 : Stereochemistry
Which of the following structures is equivalent to the enantiomer of the molecule whose Fischer Projection is shown below?
I
V
II
IV
III
IV
The compound shown is SS, so we need to look for the compound that is RR.
Example Question #13 : Help With Enantiomers
What is the Fischer projection of the following molecule?
II
I
IV
III
I
The absolute configuration of the given molecule is (amino group is R, methyl group is S). Putting the methyl group on the top and the alcohol on the bottom, this puts the amino group on the left, and the methyl group on the right. Recall that in the Fischer projection, the vertical bonds are dashed and are going into the plane of the screen/paper, while the horizontal bonds are wedges and are coming out of the plane of the screen/paper. One way to remember this is to think of Fischer projections as a skeleton (dashed vertical) wearing a bowtie (wedged horizontal).
Example Question #44 : Stereochemistry
What is the IUPAC name for the molecule shown?
S-3-methylbut-1-en-4-ol
S-2-methylbut-3-en-1-ol
R-3-methylbut-1-en-4-ol
R-2-methylbut-3-en-1-ol
S-2-methylbut-3-en-1-ol
The molecule's highest priority functional group is the group, therefore, numbering starts at the left-most carbon. The absolute configuration of the molecule at carbon is S.
Example Question #44 : Stereochemistry
What is the IUPAC name for the molecule shown?
(2R,3S)-3-methyl-2-pentanol
(2S,3S)-3-methyl-2-pentanol
(2S,3R)-3-methyl-2-pentanol
(2R,3R)-3-methyl-2-pentanol
(2R,3S)-3-methyl-2-pentanol
Carbon number : hydroxyl is first priority, The rest of the molecule is second, methyl is third. Placing in back makes go clockwise. Therefore, it is R. Carbon number : alkyl with hydroxyl is first priority, The rest of the molecule is second, methyl is third. Placing in back makes go counterclockwise. Therefore, it is S.
Example Question #21 : Help With Enantiomers
Which of the following applies to the molecule shown?
3R
3S
2R
2S
2R
Aldehyde group gets first priority; therefore, aldehyde carbon is carbon number . Aldehyde group is first priority, alkyne group is second priority, methyl group is third priority. is clockwise, so the molecule is R.
Example Question #22 : Help With Enantiomers
What is the IUPAC name of the molecule below?
S-3-butanamine
S-2-butanamine
R-2-butanamine
R-3-butanamine
R-2-butanamine
At the chiral carbon, the amino group is first priority, the ethyl group is second priority, and the methyl group is third priority. is clockwise when putting H in the back, so the molecule is R.
Example Question #21 : Help With Enantiomers
What is the IUPAC name of the compound shown?
(2R,3R)-3-propylpent-4-en-2-ol
(2R,3R)-3-vinyl-2-pentanol
(3S,4R)-3-propylpent-1-en-4-ol
(2R,3S)-3-propylpent-4-en-2-ol
(2R,3R)-3-propylpent-4-en-2-ol
Numbering of carbon chain goes from hydroxyl group (on carbon ) to double bond (carbons and ). Hydroxyl carbon and propyl carbon are both R.
Example Question #24 : Help With Enantiomers
What are the absolute configurations at carbons labelled , , and in the molecule below, respectively?
S, R, S
R, S, R
S, R, R
S, S, R
S, R, R
Carbon number : Hydroxyl is , group going up is , group going down is . Therefore it's S. Carbon number : Group going to chloride is , group going to hydroxyl is , methyl is . Therefore it's R. Carbon number : Chloride is , group going up is , group going down is . Therefore it's R.
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