i understand that the above compounds are dissymetric. but why are they not superimposable mirror images of each other? 3.how does the umbrella effect in N-(CH3)3 make it optically inactive?
391. The boiling point increases as dipole moment increases because intermolecular dipole-dipole interactions/forces add to the already present London dispersion forces. Cis isomers usually have higher boiling point because of this.
However, for melting points, intermolecular forces aren't the only deciding factor. The packing of the molecule also plays an important role.
For a thorough explanation, see this page : http://www.chemguide.co.uk/basicorg/isomerism/geometric.html
2. Try to imagine it this way. You have two open palms. On the left palm you place the structure of the left compound the way you see it on this page. On the right palm you place the structure of the right-side compound as seen on the page. Now if you try to place one palm over the other, will the two structures super-impose? The answer is no.
Thus these two are enantiomers.
3. The pyramidal inversion effect, or umbrella effect as you call it, is a spontaneous process at room temperature which operates in amines having pyramidal geometry. The simplest example is ammonia. The molecule flips inside out around nitrogen's lone pair. Since this interconversion is so rapid(the energy barrier is very small and hence the process is spontaneous), acting like a conformational change, nitrogen is prevented from obtaining chirality.
However if the nitrogen is strained (being a bridgehead atom, for example), it becomes a chiral center and it cannot interconvert.
4. Google for more about this...don't remember.
5. My guess : The left side carbon is D and the right side carbon is L, using the C-O-R-N rule.
