Substituent priority

[NonTraditional3]

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Hello,

Suppose you have a vicinal hetero dihalide subsitution on an even numbered carbon chain, where two different halides occupy the two centermost carbons - how do you determine which of the two gets the higher number?

For example:

You have a bromine and a chlorine on carbons 2 and 3 (or 3 and 2) of butane; would this be called 2-chloro, 3-bromobutane, or would it be called 3-chloro, 2-bromobutane?

 

[sciencebooks]

Hello,

Suppose you have a vicinal hetero dihalide subsitution on an even numbered carbon chain, where two different halides occupy the two centermost carbons - how do you determine which of the two gets the higher number?

For example:

You have a bromine and a chlorine on carbons 2 and 3 (or 3 and 2) of butane; would this be called 2-chloro, 3-bromobutane, or would it be called 3-chloro, 2-bromobutane?

First, you would actually not name them as you did because they should be in alphabetical order.

Next, I think bromo gets the priority because of alphabetic ordering. Halogens are all on priority together and then you go form there with alphabetic ordering.

 

[Charles Darwin]

Cahn-Ingold-Prelog:

I > Br > Cl > F > O > N > C > H

Bromine would be given priority due to its atomic weight. It also precedes chlorine alphabetically so it would be written first as well.

2-bromo-3-chlorobutane

 

[orgohacks]

Cahn-Ingold-Prelog:

I > Br > Cl > F > O > N > C > H

Bromine would be given priority due to its atomic weight. It also precedes chlorine alphabetically so it would be written first as well.

2-bromo-3-chlorobutane

This is true for determining R and S (or E and Z) but for simple naming, alphabetization wins. So if we replaced chlorine with iodine, it would still be 2-bromo-3-iodo butane.

 

[Charles Darwin]

This is true for determining R and S (or E and Z) but for simple naming, alphabetization wins. So if we replaced chlorine with iodine, it would still be 2-bromo-3-iodo butane.

That's good to know, but would something pedantic like that (sorry) be tested on the MCAT?

 

[bored]

That's good to know, but would something pedantic like that (sorry) be tested on the MCAT?

I agree its 2-Bromo-3-Chlorobutane because its alphabetic priority.

and I don't think the mcat tests for something so unimportant.

 

[NonTraditional3]

and I don't think the mcat tests for something so unimportant.

Two words my friend - Verbal Reasoning. lol