LAST MINUTE QUESTION!...simple chirality

[artmed12]

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please give your kind explanations to my sleep-deprived, weary-knee'd pre DAT a$$....


the molecules is:



CHO
CH3------C-------Br
OH

assigning priority goes: Br = 1, OH = 2, CHO = 3, CH3 = 4 correct?
MCAT 1001 organic #137 says that the CHO group is 2nd priority?

please explain....

peace and thanks

 

[artmed12]

i knew it would format incorrectly,,,,,

the CHO and the OH groups should be above and below that center carbon, respectively.

thanks

 

[_veo_]

I say you are right and so does my book..
"High atomic number takes precedence over lower"
Br = 35, OH = 16, CHO = 12, CH3 = 12.
Since CHO and CH3 have both carbon directly attached to the double bond, we go ahead and compare the other atoms.. for COH (C(OOH))and for CH3 (C(HHH)). Thus, since O is higher than H, COH is 3rd.

 

[Uracil]

the C0H is an aldehyde and when assigning priorities it counts as having 2 Oxygens bonded to the carbon atom because carbon is double bonded to oxygen, so it would be 2nd in priority.