Ring Expansion Problem

I did a write up of the mechanism for problem 12c on page 425 in ChemSketch. I hope this helps!

If you have any questions about this mechanism, please post a comment!

 

 

 

Edit: I just looked at the answer for this mechanism in the solutions manual, and the only difference is that instead of writing H-Br in the first step, they use H3O. This makes sense because H-Br is a strong acid, which means it would completely dissociate in water.

Tips for tomorrow's Quiz

Hi All,
These are a few things we can all remember that may be helpful for the quiz tomorrow:

- Secondary and tertiary alcohols undergo SN1 with halides(can form elimination product which is converted back to SN1 product) and E1(dehydration of alcohols) reactions. Since a carbocation is formed, there is the possibility rearrangement. Ring expansions can also happen if there is ring strain(3 or 4-membered rings).

- Primary alcohols undergo SN2 with halides(no eilimination product because the halide ion is a weak base and cannot remove a hydrogen from beta-carbon) and E2 (alcohol dehydration).

-Rearrangements can be avoided if PBr3, PCl3 or SOCl2 with pyridine are used instead of HBr, HI, or HCl with ZnCl2 with heat.

- SN2 reactions leads to inversion of stereochemistry, but double inversions can restore the molecule to the same sterochemistry as the starting material.

-Phosphoric and sulphuric are commonly used for dehydrating alcohols.

- In dehydration, -OH and a hydrogen from a beta carbon is removed to form an alkene. Since the reaction is heated (distillation) to remove water which is a product, the reaction is displaced to the right so that hydration does not occur(Le Chatelier's principle).

- For chromium oxidation, adding excess chromic acid to primary alcohol forms carboxylic acid instead of stopping at the aldehyde stage. However, PCC can stop this reaction at the aldehyde stage.

-Secondary alcohols normally form ketones. 

I know this does not cover everything we have done so far, but I hope it helps.

Thanks!

For my first post, I would like to thank everybody on the blog who showed up with study tips and "cheat" sheets for the reactions and mechanisms.

Organic chemistry is a class that is difficult for students who have all of their faculties, but imagine the obstacles for a student with Post Traumatic Stress Disorder. Enter my life.

I have been dealing with PTSD from an incident in the Army, and the symptoms are all counterproductive to succeeding in this class. I will spare you the details, but I need every edge I can get my hands on to get the grades I want.

I am eager to learn, and would appreciate any other study tips you may have. This weekend, every minute that isn't Superbowl Sunday I will be working on gaining a better grasp of the material we learned in chapter 9 and 10.

Chapter 10 #38

What follows are answers for problem 38 from Chapter 10, Bruice. I am including notes that indicate where special attention must be paid to each reaction.

a) This is the cleavage of an ether into two compounds, an alcohol and an alkyl halide. The formation of the major product depends on the stability of the leaving group. A tertiary carbocation is capable of forming, so the halide ion combines with the carbocation. The hydroxide combines with the methyl group.

b) This situation is also an ether cleavage, except in this case we cannot form a tertiary carbocation. The halide attaches to the less sterically hindered group.

c) This case is a dehydration of an alcohol. The reaction forms a carbocation, then undergoes a 1,2 Methyl Shift. The final result is an alkene.

d) This reaction is the oxidation of a primary alcohol. The clue for this reaction is the presence of Chromatic Acid. Because the alcohol is primary the reaction proceeds to the formation of a carboxylic acid.

e) This reaction is the nucleophilic substitution of an epoxide, occurring under acidic conditions (as indicated by the presence of HCl). Under acidic conditions the nucleophile attack occurs on the more substituted carbon. The hydroxide attaches to the less substituted carbon.

f) This reaction is also a nucleophilic substitution of an epoxide, except this reaction occurs under basic conditions. In this case the nucleophile attacks the less substituted carbon, based on lesser steric resistance from the lower degree of substitution.

g) This reaction is the activation of an alcohol and subsequent synthesis. TsCl ultimately becomes the leaving group, and is replaced via SN2. This means that the stereochemistry changes.

h) This reaction is the oxidation of a secondary alcohol. Because the reactant is a secondary compound the reaction stops with the formation of a ketone.

i) This reaction is the elimination reaction of a quaternary ammonium hydride. This reaction is an anti-Zaitsev reaction; the hydrogen is removed from the least substituted carbon. Ammonium ions function very similarly to akyl flourides. The leaving groups are more basic, and therefore create a partial negative charge on the carbon in question. This creates a "carbanion" like effect.

Edit (2/2/13): Removed the previous notes and replaced with easier-to-read copy in pen.

Ch. 10 problem 52

The problem asks you to propose a mechanism for the given reaction using only the reagents given:H2SO4 and heat.

First, We want to make one of the Hydroxyl groups a better leaving group. Sulfuric acid will protonate the Hydroxyl group so that later in the mechanism it can leave as water.

Since primary alcohols are present, an SN2 reaction will occur in the next step since a primary carbocation will not be stable for an SN1. In this step, the electrons of the oxygen of the hydroxyl group that was not protonated will attack the alpha carbon of the protonated hydroxyl group and the protonated hydroxyl group will leave as the leaving group, forming the ring-like structure. (This is a concerted reaction)

During the final step, water deprotonates the oxygen, completing the epoxide ring formation.

Below is a picture of the mechanism.

Study Tips - Organic Functional Groups

In the past, I had problems remembering functional groups in Organic Chemistry. Either I wrote them down and lost my notes or forgot to memorize them and found myself cramming before each exam. To get around this obstacle, I bought manilla folders for each class and started writing any pertinent information on the outside of them. For Organic Chemistry, this meant writing down functional groups and any molecules that were often referred to by their common names instead of their IUPAC names.

During each class or when I'm studying, I pull out my manilla folder and place it down beside me. Although this sounds trivial, it accomplishes two things:

1) It functions as a quick reference any time I need to review a functional group that I can't remember. It also eliminates the need to carry around a 20 lb. Organic Chemistry book everywhere I go, which tends to be cumbersome and definitely not attractive to those in the outside world.

2) It helps me stay organized and keeps everything in one place. Whenever looking at the structure of a functional group isn't enough, I can reach inside the folder knowing I'll be able to find my notes. This saves time, especially since I no longer have to scavenge through my car, my house, or any number of places where miscellaneous notes tend to end up.  (Murphy's Law & Entropy)

Epoxide sapling question

I was having a little trouble with sapling problem #17 which is an epoxide reacting with H2O and Hydronium.  After reading the section in chapter ten I did work it out and get the right answer but im not positive about the mechanism, I just kinda guessed it would add another alcohol group given the reactants and got lucky.  I think the H3O protonates the oxygen, then from there I have some ideas, but if anyone knows for sure how that mechanism works I would appreciate any response.

ChemWiki

I found a great resource through UC Davis: http://chemwiki.ucdavis.edu/

It's a wikipedia-like website that's incredibly easy to navigate. Not only does it have organic chemistry information, it also has sections in general chemistry (for those of us reviewing for the MCATs). Sometimes learning from an alternative source helps me studying, and this is a great one. It color-codes reactions so your eyes don't get tired looking at them. Here's a sample from their alcohol hydration page:

http://chemwiki.ucdavis.edu/Organic_Chemistry/Alcohols/Electrophilic_Hydration#Mechanism_for_3.c2.ba_Alcohol_(1.c2.ba_and_2.c2.ba_function_the_same_way).3a

I think the coolest part about this website is that they're developing a gaming system that helps students do practice problems. According to the SARIS website, students will be able to track which parts of problems they get wrong so they study more effectively. When a student gets a question right, they get "XP", a point system that allows them to level up in the game. Cheesy as it sounds, I could definitely see myself playing for practice - and points. I'm competitive! Here's the link if you want to read more:

http://chemwiki.ucdavis.edu/uSARIS

Hope this helps!

Problem 54 a

Hey guys!
If some of you are like me, then synthesis problems can be pretty difficult.  I never know where or how to start! I've been practicing some problems and I've completed Problem 54a on page 408.  It's kind of similar to the last quiz we just took.  I hope this helps!

PGM

Quiz prep

I've attached a link to a quick reference I made for the Chapter 10 reactions we have reviewed so far.  Happy studying :)

Rxn Cheat Sheet

Mechanisms: Ring formation in Acid-Catalyzed Reaction

In Chapter 10 of Organic Chemistry (Bruice), there is a practice problem that requires the use of H2SO4 in order to create THF (Tetrahydrofuran) and H2O. The starting material(SM)  is 1,4-Butanediol.

The trick to this is remembering that because the SM only contains sigma bonds that it's able to rotate and spin around.

Step 1:

*Remember because there is only 1 Equivalent they both won't do the same thing.

First protonate a hydroxyl group. This will form water with a positive charge.

Step 2:

The electrons on the remaining hydroxyl will be attracted to the positive H2O (Leaving Group)

Step 3:

Lastly Oxygen should be bonded to the terminal carbon on the opposite side of the molecule.

Water being an awesome base will pull of the remaining Hydrogen that is attached to the carbon resulting in the Final Product!


Happy Studying!!

- Cosmo+

Synthesis

Chapter 10 problem 12b. I was trying to work this problem and I pretty much understand how oxygen was protonated to get H2O which is a good leaving group but I don't understand where H30 is coming from. What is H2S04 doing in the reaction? I will be greatful if somebody can explain this to me. Thank you.

Chemplace.com

This might seem a little redundant but last semester I barely noticed the access code in the front of the book that gave us access to chemplace.com I have been using the website since last week and it is very helpful. It has powerpoint presentations for all the chapters with examples to certain mechanisms, interactive molecular animations, practice tests/quizzes, and even flashcards. I have found it really helpful for reviewing last semesters material as well as preparing for future lectures.

Using the Software to Draw

Does anyone know how to use the software Dr.Petersen said we should download on blackboard? i cant seem to figure out how to draw with it.

The best things you can do to succeed in Organic Chemistry

Please proceed in numerical order

1. Be a certified genius
If you can actually do this please feel free to stop reading now, go home and take a nap.

2.Come to lecture EVERYDAY
The best foundation is made by coming to lecture and having everything thoroughly explained to you and the notes written in your own hand, trying to decipher your friends notes or reading through the dense textbook cover to cover is a killer. You need to know what happens and WHY it happens which is usually explained in class and may not be in the notes or well explained enough for it to sink in. Dr. Petersen really does answer questions and try her best to get everything to sink in.

3. Do sapling homework as early as possible
Try to work through the problems as we learn the material so all the reactions become familiar and repetitive  they will slowly become second nature. Take time to work through the problems slowly rather than rushing to the correct answer for credits sake. If you get stuck skip it and come back rather than giving up and getting the solution straight off, allot of time unclear areas are slowly clarified through working the other problems. Go back through sapling after your done and read the explanation of any problems you had trouble with, make sure you understand the method, don't just say you get it, explain to yourself why it makes sense.

4. Get in study groups
Two heads really are better than one, sometimes you need multiple ways of thinking about it to solve a difficult problem and if you think you get it, explaining it to someone who's struggling will make you all the stronger. The camaraderie makes it less stressful, it can help you fill in understanding gaps, catch tricky loopholes, cement foundations and you make lots of friends :)

5. Work more problems
Book problems, especially the ones embedded in the chapter readings are quite helpful for assisting in full understanding of the material, the ones at the end of the chapter can also be useful as extra practice. The exceptions and tricks in the problems will get you more than anything and nothing really prepares you for them more than having seen and dealt with them before. Purchase the ACS book for Organic Chemistry and start working it, it will help you on the material now and be good overall preparation for that scary final that is coming for us all.

6. Read the book
I really hate doing this myself, but if there is a particular area you are struggling on then anything is better than leaving it weak, it will come back to haunt you. I can't make myself read it straight through but touching on sections every once and a while is helpful.

7. Find someone who is really good at
If at least one of these people aren't in your study group then you're doing it wrong. You need to make at least one person a go to for Orgo problems, I suggest this be your study group but you need at least one certified genius on your role to move along the group when they get stuck. If you don't know one of these people find them *cough Ashleigh Musso cough* use Dr. Petersen if you have to but I guarantee finding someone who knows their stuff and is learning it for the first time is better for most circumstances.

8.Look over your own notes often
Just taking the notes isn't enough you need to look at them and study them and make sure you know what they're saying. Pay special attention to exceptions, special cases, and anytime you see a mechanism if you can't remember every step just remember the trend and general ideas enough so that you could probably work it out if you had to on the spot.

9. Look over past tests
Make sure you know EXACTLY what you did wrong on every problem, if it was a stupid mistake tell yourself why it was stupid, work the problems again, get everything perfectly clarified so that you'll never make the same mistake again. Making every mistake possible before the exams (and especially the final) and figuring out ways to avoid those some pitfalls is that main way to do well in organic chemistry; leave no stone unturned.

*I apologize for any grammatical errors, it is no accident that I am not an English major

YouTube is a great way to study?

I do not like to read the book at all. It is too long and I feel so sleepy to read after awhile. I also feel like I do not really remember that much information. So I prefer the YouTube video. There are a lot of clips   about organic reactions with mechanism and also formulas. You guys should check it out.  I think the music and nice pictures make you enjoy it better. Everybody shared their study tips so I hope mine is useful for you guys too.

Question on today's lecture.

Dr Petersen,
I wanted clarification on the example you did in class today:
For the example involving the conversion of butanol to butanal using chromic acid, I realized in my notes that we arrived at a diol by adding H+/H2O. I am trying to figure out the mechanism for the reaction, can you please explain to me?
I would also appreciate it if anybody can help me.

Hitler learns organic chemistry

I love anything funny about orgo and laughs can definitely help with studying. Here is a funny video about orgo that also may express what we feel right before a test.

 http://www.youtube.com/watch?v=Ekc1Xt6gMLs

Reactions

Here's how I study for synthesis problems. I make a list of all of the reagents that can be used and I write a little description of what it does. I've done this for probably every reaction we've learned and it seems to work for me. Hope this helps!



Something to help with remembering lectures

Since others have posted their tips for helping to study and learn reactions, I thought that I would share something that I am doing differently this semester and it seems to be helpful so far.  After class, when I get home, I rewrite the notes from that day.  This not only allows me to make them more legible and more organized, but makes you go over what you did that day.  It works better if you rewrite your notes on the same day you had class.  I feel like often in class we are going pretty quickly and for me at least, I'm busy trying to take notes but don't really get a chance to really process what we are talking about.  By redoing my notes, it helps and actually helps me remember some of what was said in class.

Synthesis Reaction Blues :(

Hey Guys,
HELP!!! I have no idea why, but I have the hardest time with synthesis reactions. When I do the Sapling homework, I breeze through them. However, I believe it is because I see the options in front of me and I know exactly how many steps I need to get to the product. But, when I do them alone and all I have is the starting material and the end product, I get stumped! Does anyone know of a source or website that lists the reagents and explicitly explains how they change or alter the structure? I think me making a notecard with all them will greatly help me!

Wishing everyone well on this course! 

Problem #12 Ring Expansion

Hey guys!  I've completed the ring expansion problem from class today (yesterday?).  I highly recommend completing it, since it took me a few moments to figure it out.  I am also currently working on (in the program, I've completed them already) the solutions to Problem #11 for those that don't have the solution manual.

It has to deal with the alcohol as a leaving group, what we've been going over the past few days.  It utilizes the method of protonating the alcohol, turning it into water (a better leaving group).  

I also wonder if anybody else got a different way to do it, please let me know!

Study Tips

Organic is a hard class in general and Organic 2 is going to be harder because we have more reactions know and understand. In Organic 1, it is already hard because I have to put out a lot of time for this class to learn the mechanisms. My teacher said that Organic 2 is going more difficult because we have to know ten times more information than the mechanisms in Organic 1. I want to develop some study tips that can be helpful for me and may be for you too.

1. Attend the lecture: This is a must because the teacher would explain everything out clearly for you step by step so you can understand it better.

2. Read the materials before coming to class: If you read the book and go over the notes from the lecture slide, you can develop question that you don't understand to ask the teacher in class.

3. Do the sapling homework and the problems in the book: Practice those problems can help you with the quiz and the test. Before the test, you can look over the sapling home works and the problems that you done to make sure that you understand everything. You should take about 2 hours every day to work on this class because this class takes lots of time. There for, making a schedule to work on the problems every day is a good idea.
For the problems in the book, I would do about 10 questions without looking at the answers. After seeing the answers, I would go over the questions with a friend to help me understand what I did wrong.

4. Make a summary page of all the materials you have learned once you done with a chapter. This is the most helpful thing for me in Organic. I would be ready for the materials and when I need to go over things before the test, I can just look at the summary and understand everything. This is also helpful for me when I am doing the practice problems because when I need to look back at a mechanism or something, I can just look through the page and find it right away.

5. Making flash cards is also a good way to study: I did not try to making flash cards last year but a friend of mine did it and she did really well in the class. I think I would try to follow her example too.

6. This is the most important thing: have a good sleep and a good breakfast before taking the test. Everybody knows that they need to have a good sleep and eat healthy meals everyday but not many do it. I think Organic is really stressful for some people, like me, so people would skip meals and/or not having enough sleep because they want to set out more time to study. Or some people like to cramp in everything before the test. Well that is not good for you and the test. I know this because I have done it before. When I went in my Organic class for my exam with an empty stomach and not enough sleep, I looked at the test and it took me a while to understand just one problem and I did poorly on that exam too. Now, I would always try to eat healthy and sleep at least 6 hours for us college student.

These study tips can also apply to other classes. My goal is to do well in Organic and other classes. I hope this would help you all in your classes also. Good luck everyone.

Producing an epoxide without using MCPBA

Hello All,
So for chapter 9 sapling problems, I found that there was a question about an epoxide synthesis but there wasn't mcpba in the options so It took me a lot of attempts to get to the answer but I still cant really get it. Can anyone explain to me how would we get an epoxide using other reagents, what are the most common ones other than mcpba and what is their mechanism.
Thank you

Suggested study tips for the class

Organic chemistry is a topic that requires time and effort put in to it inorder to succeed. Therefore I have some study tips that worked for me last semester which might work for you as well.

1) try to read the book. Reading the book is really helpful because it explain things thoroughly, it goes over stuff that the professor might not had the time to go over.
*** even if you sometimes don't have enough time to read the whole chapter, try to go over the topics that you are confused about or things that you don't really get.

2) Do as many practice problems as you can. This, in my opinion, is even more important than reading the book, because what's the point of knowing all the literature about a certain topic if you don't practice or apply that knowledge.

3) Of course go over the notes and try to go to the SIP sessions.

4) Study actively (with a pencil, a pen, a chalk...) don't just read!!! Also try to develop visual summaries like flow charts, tables, drawings etc.. as you go,  these are especially helpful for visual learners.

5) Study in groups, explain stuff to others, and clear an questions you have.

This is a website that summarizes the Sn1, Sn2, E1, E2 reactions:
http://www.freelance-teacher.com/organic_chemistry_sn2_sn1_e2_e1.pdf

These are links for some alcohol reactions:
http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch08reactionsofalcohols.html
http://www.cliffsnotes.com/study_guide/Reactions-of-Alcohols.topicArticleId-23297,articleId-23272.html


Finally, you can't gain anything without first giving something in return, so work hard and do your best :) OH and don't forget to take breaks, they are very important!!
GOOD LUCK

Synthesis questions

Ma'am,








I have some questions about synthesis problems. There are so many reactions to think of when doing these problems, what shouls be our starting point? I did well on the second quuz, but I was not confident when I saw it in from of me. I do study and read the book. Many times it feels overwhelming when I see the reaction, I don't know where to start. Any tips?
Page 

Suggestion for Study Group

One thing I know I've struggled with in O Chem at times is feeling like I'm able to follow along in class well and complete the homework.  It sometimes gives a false sense of preparation, and of course practice is always the best policy.  I know when I'm trying to study or practice by myself there is always the temptation to "cheat" and glance at notes or the text while trying to solve a problem.  It usually provides the, "Oh yeah, I get that," response.

It hasn't proven to be the best solution for me, and if anyone else is interested in forming a study group I wanted to suggest a format that I think might be effective.  I was thinking if anyone on here is interested in forming a study group, a Wednesday or Thursday time might be ideal.  By then the topics have been covered in class, and it's a convenient review right before quiz time on Friday.

As a format I was thinking each person could come with a "quiz" type question, i.e. a synthesis reaction, which they have completed and are fully ready to explain.  Each question can be distributed to the group, and allowed typical "quiz" time (5 or so minutes to complete), and then discussed.

Obviously this will work better for smaller groups, but I thought this seemed like a good place to test the interest and availability of anyone that would like to participate.  I'd be happy to coordinate times and locations, but wanted to see what the interest level was.  You're welcome to e-mail me at my student account (aelane@uncg.com).  Appreciate any feedback or suggestions as well.

Good luck, and best wishes on getting off to a good semester.

Question 1a from Quiz #1

Hello guys,

I hope it's legal to ask this question on here now that the quiz is over.  I had a question about the first reaction.  2,3-dimethyl, 4-bromohexane was reacted with ethyl oxide.  [CH3-CH3(CH3)CH3(CH3)CH3(Br)CH3CH3] + [CH3CH20-].  Sorry, I can't figure out how to do super/subscripts on here.  Anyway, problems came for me when I was trying to decide the stereochemistry of the product.  The nucleophile is strong, and we were asked to give the major elimination product, so I assume it was an E2 reaction.  The H bound to the beta-carbon with the least hydrogens is found on carbon 3.  Assuming the Br and this hydrogen are removed (forming a double bond between carbons 3 and 4), I don't believe their is a way to determine the steriochemistry of the product based on the reactant we are given.  My product was E, 2,3 dimethyl, 3 hexene because that is the most stable alkene.  But, I don't know if this is correct because what prevents it from being the Z isomer of 2,3 dimethyl, 3 hexene?  We aren't given the stereochemistry of the reactant alkyl halide.  Am I missing something with this problem? 

Thank you,

Dominick DeFelice

Reaction Routes

Hi all,

I was curious if anyone else was having difficulty in grasping why particular reaction routes were taken in some of our reactions in class and on Sapling. There sometimes seems to be multiple routes to get to the same outcome, and I am finding it difficult to always find the "correct" one. By correct, I mean the resultant product would minimize getting mixture of stereoisomers, achieving the shortest/least intensive route and preventing competing reactions with some byproducts. I seem to waste an inordinate amount of time thinking about these factors, and assume that this will pass with more practice/time.

One such case came up in class concerning the possibility of chloride ion interfering with our SN2 reaction with methoxide when converting an alcohol to an ether. In that case, we had converted the secondary alcohol to a sulfonate ester using pyridine and TSCl. Then we used methoxide in the next step, in a SN2 reaction to convert the sulfonate ester to an ether. I think it was explained well why the protonated pyridine would "trap" the chloride ion, but wouldn't that also "trap" the methoxide ion to a lesser extent? Would there be a mixture as a result?

Brian

Synthesis Reactions

Has anyone found a way to separate the synthesis reactions in a way that flows more easily. Maybe categorically? I think that after I read Chapter 10, I'm going to try to make some type of chart.

Welcome to the official class blog for CHE 352-01, Organic Chemistry II.  Students will have a chance to communicate with one another and me (KSP) via the blog while earning extra credit points.  For details on the class assignment see the assignment document on Blackboard.