[deathracer26]

Is (2-E,5-Z)-4-methylhept-2,5-diene optically active?
Is it an example of pseudo asymmetric carbon ?
Why aren't pseudo asymmetric carbon optically active ?

[Dan]

You must show you have attempted the question, this is a Forum Rule.

Is (2-E,5-Z)-4-methylhept-2,5-diene optically active?

What do you think, and why?

Is it an example of pseudo asymmetric carbon ?

What is the definition of a pseudoasymmetric centre?

Why aren't pseudo asymmetric carbon optically active ?

Optical activity is a property of a molecule, not an atom. Please clarify your question.

[deathracer26]

You must show you have attempted the question, this is a Forum Rule.

Is (2-E,5-Z)-4-methylhept-2,5-diene optically active?

What do you think, and why?

Is it an example of pseudo asymmetric carbon ?

What is the definition of a pseudoasymmetric centre?

Why aren't pseudo asymmetric carbon optically active ?

Optical  activity is a property of a molecule, not an atom. Please clarify your question.

I am sorry I didn't knew that , should have read the rules.

1)I think it should be optically active since all four groups attached to C-4 are different and because of that the molecule is asymmetric , no plane of symmetry  exist which is the requirement for optical activity .

2)Pseudo asymmetric carbon is one which have exactly two groups which are constitutionally same but structurally different(opposite) and other groups are different.

3)Sorry again.
Question - Why are molecules which have only one asymmetric carbon which is also pseudo asymmetric are optically inactive ?I understand that because of two groups with opposite structure there is internal compensation but what about the pseudo asymmetric carbon , does that carbon contribute to optical activity if the molecule ?

[Dan]

1)I think it should be optically active since all four groups attached to C-4 are different and because of that the molecule is asymmetric , no plane of symmetry  exist which is the requirement for optical activity .

I agree.

2)Pseudo asymmetric carbon is one which have exactly two groups which are constitutionally same but structurally different(opposite) and other groups are different.

Yes, the two groups differ only in their chirality sense (R/S).

Is this the case for your molecule?

3)Sorry again.
Question - Why are molecules which have only one asymmetric carbon which is also pseudo asymmetric are optically inactive ?

A centre can be either asymmetric or pseudoasymmetric, not both.

I understand that because of two groups with opposite structure there is internal compensation but what about the pseudo asymmetric carbon , does that carbon contribute to optical activity if the molecule ?

You are correct regarding internal compensation - a pseudoasymmetric centre necessarily implies that the compound is meso. The pseudoasymmetric centre doesn't cause chirality - this is why it is given a special name - because it lies on a mirror plane (between two mirror image substituents).

[deathracer26]

 Do you agree that this molecule is optically active because it have four different groups attached to it ? Since the two groups are geometrical isomers and they are separately optically inactive , I am not so sure about it being pseudo asymmetric.

If it is pseudo asymmetric then the molecule is optically inactive.

Is the mirror plane passing through the 4^th carbon important for telling whether the molecule is optically active or not.

[Irlanur]

no plane of symmetry  exist which is the requirement for optical activity .

it's not. A molecule is chiral if does not have an improper rotation axis.

[Dan]

Do you agree that this molecule is optically active because it have four different groups attached to it ?

Yes, it is optically active - it has a non-superimposable mirror image.

Since the two groups are geometrical isomers and they are separately optically inactive , I am not so sure about it being pseudo asymmetric.

We have a definition of a pseudoasymmetric centre. Does this definition fit with any centre in the molecule?

If it is pseudo asymmetric then the molecule is optically inactive.

What is "it"? The presence of an asymmetric centre in a molecule does not mean the molecule as a whole must be achiral. A molecule cannot be pseudoasymmetric.

example: Hyoscyamine


Hysocyamine has 3 asymmetric centres and one pseudoasymmetric centre (labelled 3) and it is chiral.

Is the mirror plane passing through the 4^th carbon important for telling whether the molecule is optically active or not.

The presence of a mirror plane proves achirality - but be aware that (as Irlanur points out) the absence of a mirror plane does not prove chirality.

[OrgXemProf]

I'm new to Chemical Forums (Total time logged in: 43 minutes), but I thought it might be nice to start off on the right foot by suggesting a reference that deathracer26 might find useful in the future when faced with stereochemistry-related questions.

For cogent definitions and numerous examples with detailed discussion I recommend E. L. Eliel & Samuel H. Wilen, "Stereochemistry of Organic Compounds", Wiley, New York, 1994.