[kriggy]

Hi guys, Im supposed to write R/S configuration of those compounds and Im bit stuck with A ad D. (B is not opticaly active since there is a plane of symmetry and C has S configuration)
 Are those opticaly active or not? I think that there is possible rotation between the single bond connecting those aromatic rings but Im not sure. Im glad for any help or hints

[OrgXemProf]

Please see Eliel, E. L.; Wilen, S. H. Stereochemistry of Organic Compounds, Wiley: New York, 1984:

Atropisomerism in biphenyls: Section 14-5, pp 1142-1155. Quoting from page 1143 therein: "Di-ortho substituted biphenyls are generally resolvable only if the substituents are large."

So, do NH2 and NO2 qualify as "large" substituents [example (a)]? Certainly, deuterium (C-D bond) is not a large substituent [example (d)].

Admittedly, analysis would be facilitated if your instructor had placed substituents at the 2,2',6,6' positions of the aryl rings [instead of at the 2,3',5',6 positions as they appear in examples (a) and (d).]

Cumulenes: Section 9-1.c, pp 543-544. Although kriggy didn't indicate any ambiguity with examples (b) and (c), it nevertheless might prove helpful to construct a model of each cumulene in order to assess potential chirality.

Assignment of Cahn-Ingold-Prelog (CIP) R/S configuration in molecules with axial chirality - see:
http://en.wikipedia.org/wiki/Axial_chirality

[Altered State]

Yes, they are opticaly active.

It is called "axial chirality", for the 4 examples you have posted.

For B and C, this applies: http://upload.wikimedia.org/wikipedia/commons/2/20/Allene_chirality.png

For A and D (still, for D is not so clear, since substitutents are not that large), you have to follow something like this:

[kriggy]

Thanks for replys. 
Im aware of axial chirality but I was bit confused by than 3,5 substitution and thought that the rotation will be unblocked because the groups are further away of each other.

[OrgXemProf]

It might be instructive to re-examine the analysis presented in the most recent response to kriggy's original question.

Two views of structure 2 are presented therein. Structure 2.1 is produced by viewing the molecule from left to right [i. e., observer standing at the left of the molecule looks to the right down the C(1)-C(1') bond in Structure 2 with C(1') away from the viewer]. Then, Structure 2.2 is produced by viewing the molecule in the opposite sense [i. e., observer standing at the right looks to the left down the C(1')-C(1) bond in Structure 2.2 with C(1) away from the viewer].

Since this is the same chiral molecule viewed from opposite directions, it follows that the absolute configuration of each of the two depictions of this molecule (i. e., Structures 2.1 and 2.2) must bear the same R,S descriptor!

Please consider the following quotation taken from my personal-favorite stereochemistry opus, Eliel, E. L.; Wilen, S. H. Stereochemistry of Organic Compounds, Wiley: New York, 1994, page 1130, to wit:

"Molecules with chiral axes may alternatively be viewed as helices..., and their configuration may be denoted as P or M. For this designation, only the ligands of highest priority in the front and in the back of the framework are considered. If the turn from the priority front ligand 1 to the priority rear ligand 3 is clockwise, the configuration is P (or aS in chiral axis nomenclature), if counterclockwise it is M (or aR in chiral axis nomenclature).

It is important to note that only the priority front ligand 1 and the priority rear ligand 3 are considered.

So, with the foregoing in mind, how would we designate the absolute configuration of Structure 2?

First, let's consider Structure 2.1: The turn from priority front ligand 1 in this structure (OCH₃) to the corresponding priority rear ligand 3 (NO₂) is seen to be clockwise. Hence, this structure possesses the P (helix nomenclature) or aS (chiral axis nomenclature) configuration.

Now, to check our findings by applying this same approach to analyze the absolute configuration of Compound 2 as viewed via Structure 2.2: Here, the turn from priority front ligand 1 in this structure (NO₂) to the corresponding priority rear ligand 3 (OCH₃) is seen once again to be clockwise. Hence, we have confirmed the absolute configuration of Structure 2; this structure indeed possesses the P (helix nomenclature) or aS (chiral axis nomenclature) configuration.

[Altered State]

Great explanation and great reference, even though I'm not the original poster, thank you.