adrenaline and dopamine

in organic compounds, under room temperature, usually only sp3 hybridized carbon atoms can act as chiral centres. And the criteria is that all the four groups attached to that carbon are different and that make this centre have no internal mirror plane.

So apparently dopamine is non chiral. As there is no sp3 hybridized carbon with four different groups.

But in adrenaline, there is one chiral centre, actually it was indicated by an R letter on that carbon in the picture u provided. The meaning of R is defined by using the Cahn-Ingold-Prelog priority rules.

And for nitrogen atoms, they are also sp3 hybridized. In adrenalin, the nitrogen atom also has no internal mirror plane. But it is not chiral under room temperature as room temperautre gives the nitrogen enough energy to flip over the lone pair and become the another enantiomeric form and the two forms can't be resolved. So only under 100K, a nitrogen atom can become chiral.

Just adding on to what the previous poster said -
For something to be 'chiral', there must be a 'chiral centre' as you already know. A 'chiral centre' or 'chiral carbon' as we are most interested in all the time is a carbon atom that has 4 different things attached to it.
For dopamine, there are no chiral carbons, thus, it is 'achiral'.
For adrenaline, it's already indicated on the picture with the letter 'R' (a right hand turn). Therefore, it's 'chiral'. And there's only one chiral centre here.
However, I wouldn't say the NH2 is chiral, whether it's at room temp. or not because you still need 4 different functional groups attached to it to make it 'chiral'. The lone pair can be delocalised onto the C-N bond, which doesn't make it chiral at all, just a resonance structure between an amine and imine.
Hope that makes sense.

2007-05-09 02:46:04 補充：
Ahh..did I say NH2? Of course, as you may already noticed, adrenaline has a methyl group on the N atom, not a H! So in which case, the N atom is chiral - just like the 1st poster said.

2007-05-09 02:53:14 補充：
Yes it's true that the stereochem can be 'flip' without much energy in put - and thus, giving rise ( ) and (-) forms of adrenaline.

2007-05-09 02:53:37 補充：
However, these enantiomers CAN be separated, with a lot of work involving chiral HPLC columns. The pure enantiomers are commerically available - check Sigma Aldrich for details.