[CrazyAssasin]

I was given a problem to explain why different reaction pathways make products having different specific rotations( I attached the reaction mechanisms). I think of Tosyl group as steric hindrance which might convert enantiomers. But it is just my prediction. Actually I am not very good at stereochemistry and I would appreciate your help.

[discodermolide]

What kind of reaction mechanism is the top one (with ethanol)?
What is the bottom one (with ethyl bromide), in terms of mechanism?
This is only partly about stereochemistry, I think they are asking what I did as well.

[CrazyAssasin]

The first one is Sn1 and the second one Sn2 reaction. In the Sn1 reaction the ethanol can connect cation from two sides so it supposed to be a racemic.

[Dan]

In the Sn1 reaction the ethanol can connect cation from two sides so it supposed to be a racemic.

The non-zero optical rotation proves that it is not purely S_N1.

[discodermolide]

Lets talk about the top line. alcohol - tosylate-ethyl ether.
Which reaction type is this?

[CrazyAssasin]

Well it should be Sn1 because TosO- is very good leaving group and ethanol isn't very good nucleophile but if it was true cation would rearrange to become more stable and ethanol would connect to carbon closer to benzene. However it doesn't so it is Sn2 mechanism but I can't find a reason why.

[discodermolide]

You don't think that at temperature it is an S_N2 displacement with ethanol?
The difference in the rotations is only about 3°, not too much difference. Perhaps there is some S_N1 character to this reaction causing some racemisation.