[RonRa]

In David Klein's "Organic Chemistry" textbook, p. 171, figure 4.28 ...
http://books.google.com.au/books?id=SsX9pbarkQkC&pg=RA1-PA171&lpg=RA1-PA171&dq=figure+4.28+Klein+Organic+Chemistry+1,3-diaxial+interactions&source=bl&ots=elBW9Oh_N7&sig=cmd81AqZPCXWLJh5YZIFabecKuw&hl=en&sa=X&ei=PRW9Uf7lKOOkige_1IG4Aw&ved=0CCwQ6AEwAA#v=onepage&q=figure%204.28%20Klein%20Organic%20Chemistry%201%2C3-diaxial%20interactions&f=false
... there are two hydrogens drawn on carbon-3. Shouldn't one of these hydrogens point straight up, (and the other one hidden behind its carbon)? ...because that's what I see when I use my modelling kit.
thanks.

[orgopete]

In David Klein's "Organic Chemistry" textbook, p. 171, figure 4.28 ...

... there are two hydrogens drawn on carbon-3. Shouldn't one of these hydrogens point straight up, (and the other one hidden behind its carbon)? ...because that's what I see when I use my modelling kit.
thanks.

You are correct. None the less, I'm sure Klein was more interested in preserving the identification of the CH2 group by drawing it in this awkward fashion than leaving one hydrogen hidden. The discussion is about the illustrated interactions, hence if you rotate the structure, that CH2 group now becomes one of the front groups of the Newman projection and those same hydrogens are axial and equatorial as being inquired.

[RonRa]

Thank you so much.

Can I just say, if the equatorial hydrogen of that CH₂ group is not involved in any diaxial interaction, I'm not sure why it needs to be shown at all, let alone incorrectly.

Klein draws the axial hydrogen of that CH₂ group on an angle (instead of vertically) and says it is gauche to the methyl group. But it is not gauche, is it?; it's not on an angle, and the two carbons aren't even directly connected. It's just a different type of steric hindrance.

[TwistedConf]

Klein draws the axial hydrogen of that CH₂ group on an angle (instead of vertically) and says it is gauche to the methyl group. But it is not gauche, is it?;

The linked explanation is overly confusing, and actually wrong in a way.

The axial methyl in THIS COMPOUND is disfavored because it's gauche to the adjacent ring CARBON (no need to even get too caught up in those CH2 hydrogens). When it goes equatorial, it's anti to the same ring carbon. Make yourself a model.

But this example isn't really showing a significant 1,3-diaxial interaction. Draw both chair forms of cis-1,3-dimethylcyclohexane. The one where they're both axial is a case where those methyls can almost touch each other, and represents a more clear 1,3-diaxial STERIC interaction.

[RonRa]

That makes sense to me. Thank you.