Tutor.com Organic Chemistry Session

Jun. 27, 2013

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Session Transcript - Science - Chemistry, 6/26/2013 8:33PM - Tutor.comSession Date: 6/26/2013 8:33PM
Length: 26.1 minute(s)
Subject: Science - Chemistry


System Message
[00:00:00] *** Please note: All sessions are recorded for quality control. ***

Guest (Customer)
[00:00:01] All of the following substituents are deactivating; some more than others. Only one of the substituents, however, is a meta-directing group. Which one?

Rey m (Tutor)
[00:00:08] Hi
[00:00:11] This is Rey.
[00:00:16] How are you?

Guest (Customer)
[00:00:30] Im doing good! I need help with a question. I posted it on th eboard
[00:00:49] I think im suppose to be looking for themost electronegative one?

Rey m (Tutor)
[00:01:05] I'm sorry, but this question is out of my area of expertise.  So I don't take up too much of your time I will transfer you to the next available tutor for help with this problem. Would that be OK?

Guest (Customer)
[00:01:19] yes

System Message
[00:02:06] *** The session has been transferred. ***

Paul B (Tutor)
[00:03:09] Hi, I can see your question on the whiteboard, give me a quick second while I do a bit of research

Guest (Customer)
[00:03:23] great thanks

Paul B (Tutor)
[00:04:47] Okay, can you tell me if you have any initial ideas about how to solve the problem?

Guest (Customer)
[00:05:20] yes. I believe we are looking for the most electronegative one. Which Im thinking is flourine

Paul B (Tutor)
[00:06:53] Your thinking is along the right lines, but fluorine is not the right answer, since "direction" is not a function of just electronegativity.

Guest (Customer)
[00:07:22] okay?
[00:09:02] im not getting what your saying?

Paul B (Tutor)
[00:11:03] The o,m,p directing of a group (like fluorine) is dependent on whether or not the group can stabilize a cation on the carbon which the substituent is bonded to. I'm going to draw a picture and paste it in in a few seconds.
[00:13:17] I'm working on this...
[00:15:45] Okay, this step shows the first part of the reaction mechanism for ortho addition.
[00:16:47] What I was referring to before, was the cation I've circled in red. If the substituent (F) stabilizes this cation, the products will be a mixture of o, and p.
[00:17:29] Fluorine and chlorine can stabilize such cations, because they are able to donate electron density through their lone pairs.
[00:18:05] Does that make sense?

Guest (Customer)
[00:18:09] yes.
[00:18:23] so you think it's chlorine?

Paul B (Tutor)
[00:18:47] no, I think that both F and Cl are ortho para directors, not meta

Guest (Customer)
[00:19:01] OH OH...yes yes. I see okay.

Paul B (Tutor)
[00:19:17] Good That leaves us with choices c,d, and e

Guest (Customer)
[00:19:37] correct. And sorry, i miss read what you had typed last.

Paul B (Tutor)
[00:19:44] Its okay
[00:20:26] Now, again, with these last three substituents, the correct answer should be the choice which would least stabilize the circled cation.

Guest (Customer)
[00:20:42] Well, both answers d, and e have a lot of chlorine in them. So C?

Paul B (Tutor)
[00:21:39] In this case, the chlorine will not be able to donate electron density through its lone pairs, because it is two atoms away from the cation. The biggest impact is from elecronegativity.

Guest (Customer)
[00:23:01] so e?

Paul B (Tutor)
[00:23:37] Thats right!
[00:23:42] Does that make sense?

Guest (Customer)
[00:24:09] yes. Chlorine is the most electronegative and e has the most of it

Paul B (Tutor)
[00:25:08] yes! have you learned a concept called hyperconjugation in class? That also helps explain the choice between c,d, and e.

Guest (Customer)
[00:25:35] see, we havent. Thats why I have no idea why the heck this question is in our homework

Paul B (Tutor)
[00:26:09] Okay, it is much easier to determine the correct choice between those three with that concept in mind.

Guest (Customer)
[00:26:26] Ill have to ask my prof about it tmorrow. Thanks for your help