R.S Cahn/Ingold Nomenclature Help

[Sslsn]

Here is the problem: http://i.imgur.com/Eltwj.png

I understand the nomenclature rules but this problem has been confusing me. From my understanding, the CH2NH2 would have a higher priority than the CN, because of the hydrogens. This wold mean that if I rotated the lowest priority back (the #4 hydrogen shown in the pic below), it would be S. But the answer key says that the CN has higher priority than the CH2NH2, and that the configuration is R.

Here is my attempt: http://i.imgur.com/gbxnA.png

thank you

 

[ChiralWaltz]

Functional groups have a different set of priority rules.

http://www.lavcchem212.com/files/FGPR.PDF

 

[Sslsn]

I'm going to assume we have not learned yet (It's not even mentioned in the chapter). Is this common in an organic chem class?

 

[ChiralWaltz]

My prof doesn't test over it. This is a good resource for O chem I

http://www.lavcchem211.com/downloads.html

 

[Saitama]

There is a rule about assigning priority when there are double and triple bonds in the substituents. Ever heard of that?

 

[Sslsn]

yes, but there are only single bonds in that problem

 

[Saitama]

CN has multiple bonds.

 

[Sslsn]

is there a way to determine that without going through formal charges?

 

[Saitama]

Formal charges? Why are you talking about them here? See the structure of CN and use the rule i said a couple of posts ago.

 

[Sslsn]

how can you easily tell if the bonds in the diagram are single double or triple (C=N and not C-N)?

 

[AGNuke]

Just try to satisfy the valencies of the respective atoms + A little textbook wisdom will do. Most of the bonds can easily be determined just by valency, but some may deceive, especially the co-ordinate bonds. That is where you jot them down and learn them.

In chemistry, life can be much simpler if you just rote learn some exceptional cases. Saves you the trouble.

 

[Sslsn]

i thought multiple bonds would be given, and to just assume they are all sigma if not.

but i guess not

 

[ChiralWaltz]

i thought multiple bonds would be given, and to just assume they are all sigma if not.

but i guess not

O Chem is a good place not to make assumptions, especially in the early stages. The rules are semi intuitive but are still made by man. Ask yourself questions about what you are looking at. Learning to recognize functional groups as they are written in the -COOH and -OH form or carboxylic acid and hydroxyl *might* help you see what you are looking at without having to count electrons and formal charges. Will you be taking the second semester?