Classifying carbons

[BradyC]

---

Members don't see this ad.

Hello,

I just completed a set of problems from TBR Orgo I book Chapter 4. This chapter covers alkanes. One of the problems (#9 from the 25 Question set) gave us three sex phermones and asked to pick which one had the most primary carbons. I thought that this was pretty straightforward and now am very confused. All three molecules are straight chain so they each have at least 2 primary carbons. The correct answer choice (2-methylheptadecane) has three primary carbons due to branching, which I counted identified. However, I selected the molecule (E)-8-dodecen-1-yl acetate as the correct answer and said it had 4 primary carbons. My question is does the classification system only address sp3 hybridized carbons? What about sp2 and sp Carbons? I said that the carbonyl carbon of the ester bonded to two Os and one methyl group was a primary carbon. In addition, I said that the carbon directly bonded to the O of the ester (straight chain) was also a primary carbon since it is bonded to the O, 2Hs and 1C. How come that C is also not considered when classifying carbons? Any assistance would be very much appreciated. Thanks.

 

[Czarcasm]

This is an interesting question, and I'm curious to know what someone with higher organic background has to say.

Generally though when I solve problems like these, I take a very simplistic approach. I focus exclusively on c-c bonds and disregard any carbon atom bonded to a heteroatom like oxygen.

Therefore, all the carbons at the very end will be CH4 (and thus primary), while those in the middle will be methylene groups (CH2) bonded to two other carbons and therefore secondary -- those bonded to 3 other carbons are tertiary.

Personally, if you had time, I'd post this question on coursesaver.com and ask Chad or, contact James from masterorganicchemistry.com. Both are extremely knowledgable people that would probably give you a better answer than me, haha.