SN1 reaction question?

[cheepcheep]

Hey guys! I'm *attempting* to self study OChem for the PCAT and I came across a problem with SN1 reactions. I tried looking up the answer online, but I keep getting different things!
My textbook says that a SN1 reaction results in a loss of optical activity (which could or could not be due to racemization of the solution?). However, there is a higher chance of inversion than retention. If that is so, where do SN1 reactions result in a loss of optical activity (since the solution would not be a racemic mixture)?

---

Members don't see this ad.

 

[Rouelle]

Hey guys! I'm *attempting* to self study OChem for the PCAT and I came across a problem with SN1 reactions. I tried looking up the answer online, but I keep getting different things!
My textbook says that a SN1 reaction results in a loss of optical activity (which could or could not be due to racemization of the solution?). However, there is a higher chance of inversion than retention. If that is so, where do SN1 reactions result in a loss of optical activity (since the solution would not be a racemic mixture)?

This is somewhat of an oversimplification, but here goes:

1) Sn1 reactions are said to lead to racemization because when a leaving group (eg. halide ion or other) dissociates from a chiral carbon, then the resulting carbonium ion is sp2 hybridized and trigonal planar. Thus an incoming nucleophile can add to either side of the plane, resulting in 2 possible enantiomers.

2) Inversion is more common because, although the leaving group dissociates from the carbon, it ultimately does not go very far (eg. it forms a tight ion pair because there still exists an electrostatic attraction). Thus the leaving group is hanging around partially blocking the side of the carbon it came off of and the more free side for the nucleophile to attack is on the side opposite the leaving group. Thus inversion occurs to some extent.

3) Yes, some racemization can occur simply from solvation. This is, however, probably going into more detail than you might see on the pcat.

 

[ChEStud]

I doubt the PCAT goes into details about reactions and synthesis so I doubt stuff about SN1 won't be on the PCAT. Correct..?

 

[deleted437652]

I doubt the PCAT goes into details about reactions and synthesis so I doubt stuff about SN1 won't be on the PCAT. Correct..?

I just took one of the official pearson practice tests and they had a couple questions about synthesis. Mostly simple stuff, like going from alkene to alkane, but they did have one that wasn't as readily obvious.