[pfnm]

A question in an online assignment asks:

which of the following compounds DO NOT contain a plane of symmetry?

(i) propanal
(ii) (R)-2-chlorobutanoic acid
(iii) 1,4-dioxane
(iv) oxirane
(v) cyclohexanone


Choices:

a - (i) only
b - (ii) only
c - (i) and (iii) only
d - all of the above
e - none of the above

----

The last 3 compounds have symmetry planes. (R)-2-chlorobutanoic acid does not.

But what about propanal?

If I choose answer b, it would imply that propanal does have a symmetry plane. This seems the wisest answer but I don't know . I've tried drawing it several different ways and can't see the plane of symmetry (in propanal).

Thanks

[Dan]

I've tried drawing it several different ways and can't see the plane of symmetry (in propanal).

Don't forget the plane of the page you are drawing on!

[pfnm]

Ah right ... yep I see the plane of symmetry in propanal now, I've drawn it and (R)-2-chlorobutanoic acid using ChemSketch:



I have some trouble knowing the conventions of drawing organic structures - besides using bold and dashed lines, they've never really been taught to us. I just sort of copy what I see.

(For example, using 'skeletal structures' like in the image, I've drawn the leftmost carbon 'down'. But I could draw it up, then angling down, then going up...is there a rule for this? Must the leftmost carbon, using skeletal drawings, be down, or up, or does it not matter?

Also when drawing structurs with double bonds and assigning E/Z config, I use C=C then draw the substituents on hashed or bold bonds, but 'seeing' the tetrahedron on certain carbons can be confusing, and it can also be confusing when drawing complex structures....eg (3S,4Z,8S)-4-decene-1,3,8-triol was one I had to draw for this assignment.)

The problem asked, 'what is the major product resulting from the reaction of (3S,8S)-4-decyn-1,3,8-triol with Hydrogen gas and a poisoned (Lindlar) catalyst?

To show the 'syn' addition, I drew it like this (after multiple tries...and with a somewhat confusing endproduct that I've had lots of trouble drawing in an exam I think)





Is there anywhere that has rigorous instructions on drawing organic structures?

Thanks alot