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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: bashmaster on October 20, 2005, 08:13:51 PM

Title: how many primary carbons are there in this structure
Post by: bashmaster on October 20, 2005, 08:13:51 PM
Hi guys! I got my first test back today and one the questions was, "how many primary carbons are there in this structure"  A primary carbon to my knowledge, is a Carbon Bonded to another Carbon, and 3 other noncarbon atoms.  However, I got this question wrong. One part of the question had a "C-O-CH3" and he said the "C" in the "CH3" was a primary carbon, but it is NOT BONDED to any other CARBON!! He stated: "ALL METHYL GROUP CARBONS are PRIMARY CARBONS" Is this true?? (the C on the methyl was bonded to the O, the other to the H's)


(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fimg476.imageshack.us%2Fimg476%2F921%2Funtitled6pl.png&hash=0701ccb5a8ded5c9150ac577d79e3aa3)

The concept of "a primary carbon is a central carbon bonded to ONE other carbon" is not a very hard concept to understand.  However then, can it be true, that the circled carbon in red can be a primary carbon?

I KNOW that CH3 is a methyl...can anyone answer?
Title: Re:I believe my professor may be wrong
Post by: asdf on October 20, 2005, 10:22:54 PM
first post here.

i just did a quick google search since i don't have my organic textbook anywhere close and found this.

http://www.personal.psu.edu/faculty/t/h/the1/nomencl.htm

Quote
These prefixes refer to the degree of alkyl substitution ("secondary" of "tertiary") on the carbon that is missing a hydrogen atom. These terms are not limited to use for alkyl groups, however. The degree of alkyl substitution for any carbon atom can be specified. There are four possibilities: carbon atoms that are connected directly to only one other carbon atom (i.e., connected to one alkyl group!) are referred to as "primary" (1°); carbons directly attached to two adjacent carbon atoms are "secondary" (2°; also abbreviated "sec-" or just "s-"); a carbon with three attached carbons is " tertiary" (3°; also abbreviated "tert-" or just "t-"); and carbon atoms that are fully substituted by direct attachment to four other carbon atoms are called "quaternary" (4°).
Title: Re:I believe my professor may be wrong
Post by: mike on October 20, 2005, 10:55:32 PM
The molecule you circled isn't primary, but what about the other methyl groups attached to the tertiary carbon?
Title: Re:I believe my professor may be wrong
Post by: movies on October 21, 2005, 12:42:19 AM
The IUPAC site seems to agree with your professor.

http://www.iupac.org/goldbook/A00228.pdf

Assuming R doesn't have to be alkyl.  However, if that's the case then one would assume the central carbon of isopropanol would be tertiary, which it isn't.

The way I learned it was that the only carbon that wasn't primary, secondary, tertiary, or quaternary is that of methane, where it is formally zero.  I think any organic chemist would call that carbon primary.  The definition doesn't seem too well thought out.

I tend to think of carbon in terms of oxidation state, it avoids most of these problems.
Title: Re:I believe my professor may be wrong
Post by: mike on October 21, 2005, 12:47:54 AM
So would you call the carbon I circled primary then?

It is confusing.. :)
Title: Re:I believe my professor may be wrong
Post by: mike on October 21, 2005, 12:50:09 AM
What about haloalkanes?

H3C-Cl is this primary? shouldn't be should it?

H3C-CH2-Cl this is the primary version right?
Title: Re:I believe my professor may be wrong
Post by: bashmaster on October 21, 2005, 02:12:15 AM
From many many sources, I found he is indeed wrong, however, I dont know how to go about handling it.  I do not know if I should talk to him about it or not.
Title: Re:I believe my professor may be wrong
Post by: AWK on October 21, 2005, 02:32:31 AM
According IUPAC definition cited by Movies CH3 is outside this type of nomenclature.
But note
CH3NH2 is a primary amine (now we count organic  groups at nitrogen atom)
Title: Re:I believe my professor may be wrong
Post by: Garneck on October 21, 2005, 04:56:23 AM
Well, according to IUPAC, R is everything besides hydrogen.. so I guess in that case yor methyl group is primary. Although.. I myself would have doubts about it.