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Keto-Enol Tautomerism

Keto-Enol Tautomerism

 

Keto-Enol Tautomerism is a process where an equilibrium occurs between the keto form (ie a normal-looking ketone) and the enol form (a double bond adjacent to an alcohol) of a carbonyl, acheived through the movement of atoms and breaking of single bonds.

Spoiler alert: In most cases, the keto form is highly favored.

What is the keto form of a carbonyl? The keto form is what you are used to looking at. It is any normal-looking aldehyde or ketone, in which there is a carbonyl and hydrogen atoms alpha to the carbonyl.  See below:

What is the enol form of a carbonyl? The word “enol” can be broken down into two parts: “en” (pronounced “een”) as in part alkene, and “ol” as in part alcohol. The two parts, the alcohol and alkene, come off of the same carbon atom. See below:

What is this crazy thing called tautomerization? Tautomerization is a process where single bonds are broken and atoms are rearranged to give a different structure.  This is different from resonance structures, where you NEVER break a single bond. In Keto-Enol Tautomerism,  a carbonyl double bond is broken,  an alkene double bond is formed, and a hydrogen atom migrates from the alpha carbon to the oxygen atom, forming an alcohol.

keto-enol tautomerism

What is this equilibrium you speak of? Remember, that energy within the solution can cause structures to form which aren’t the most thermodynamically favored. This is what is happening here. There is an equilibrium between the keto and enol form, almost exclusively favoring the keto form. However, the enol form does exist in solution.  The ratio of keto to enol forms depends on several factors, which we will discuss further below.

When is the enol form more favored or the major form?  We think there are four situations where the enol form is more favored (but not necessarily the major form) you should learn.

  • Situation 1: When you get conjugation out of it.  Conjugation will mean more enol form.

  • Situation 2: When you get increased hydrogen bonding.  (and in this case, some conjugation too)  This one is sweet because the hydrogen-bonding makes a six-membered ring.

  • Situation 3: When you can get aromaticity out of it.  In this case, there is nothing but the enol form.

  • Situation 4: If you can get a more substituted alkene.  There will be more of B in the enol form than A, but still not a ton of B.  There will be more of B in the enol form in its equilibrium because tetra-substituted alkenes are more stable than di-substituted.

 

 

 

 

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Epoxidation of Alkenes [with free study guide]

Epoxidation of Alkenes

Somewhere in one of your exams, you will see at least one question on epoxidation of alkenes.

The reaction:  What is epoxidation? An epoxide is a 3-membered ring containing two carbon atoms and one oxygen atom. It is interesting because it is easily opened due to small ring strain and due to the electronegativity of the oxygen atom.

epoxide

The reagents and starting materials:

1) What is an alkene?  An alkene is an unsaturated hydrocarbon containing at least one double bond.

 

2) What is epoxidation of an alkene? This is the reaction where an alkene is subjected to a peroxyacid to convert it into an epoxide. Another way to say it is epoxidation is the electrophilic addition of oxygen to the double bond of the alkene.

 

3) What reagents can you use to create the epoxide? Generally, peroxy acids are used in this electrophilic addition to the alkene. There are several types of commonly used peroxyacid such as proxy trifluoroacetic acid, peroxyacetic acid, hydrogen peroxide, and mCPBA.

 

 

The mechanism: The mechanism for the reaction is relatively complex.   While it is considered a single step reaction, it involves several changes. The double bond is our nucleophile and attacks the more electrophilic oxygen. This breaks the weak oxygen-oxygen bond and creates a new carbonyl. Once this carbonyl is formed, rearrangement occurs and the more electrophilic oxygen is released to become the oxygen of the epoxide.

mechanism of epoxidation

The stereochemistry: The stereochemistry associated with this reaction is interesting and important. As the reaction can occur on a cis or trans alkene, we see the two different products come from these two different starting materials. The oxygen can only attack from one face of the alkene. This means that the stereochemistry of the alkene is retained. Translation: if you start with a cis alkene you will get a cis epoxide. If you start with a trans alkene, you will get a trans epoxide.

epoxidation of alkenes

Further, remember that if you start with a di or tri-substituted alkene, you very well may create new stereocenters. However, if you remember the golden rule of chirality, you will know that  you need to start with chirality in order to finish with it. These alkenes are not chiral to start with, therefore we will end with a racemic mixture. If there is some chirality in the molecule, somewhere near the double bond then that chirality can influence which face the peroxyacid is attacked from, but will not exclusively give a chirally pure product.

The reaction the reaction is versatile, and works on many different alkenes. Please remember that the reaction will not work on the double bonds of an aromatic compound.

Some examples:

 

 

 

 

 

We rate the importance of this reaction, the epoxidation of alkenes, as four beakers out of five.

 

 

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Newman Projection Practice Problems [with free book]

 

Newman projection practice problems

 

When looking at Newman projection practice problems, there are a few areas that we need to make sure that we emphasize so you see the entire range of problems that might appear on an exam. First however, we should do a brief review on Newman projections. To see a full review of Newman projections, see this previous blog post. Briefly, Newman projections are a way to view simple organic molecules by looking at down the axis between two carbon atoms. We show the carbon atoms as little balls and the substituents as sticks coming off those balls at 120 degrees away from each other. There are three primary configurations a Newman projection can be in: staggered, eclipsed, and gauche. Below you can see examples of each one of these.

Now that we know what a Newman projection is, let’s look at what the most common types of questions you will see are:

 

Problem #1: Can you draw a Newman projection?  Draw the Newman projection of butane.

This is the most basic of Newman projection practice problems. All you have to do to master these problems, is find out where the axis of interest is. Please note, this is much different than the axis of Evil.

Generally, the main axis, or axis of interest, or carbon-carbon bond of interest will be a central carbon bond in your molecule. For example, in butane the most common axis for Newman projection is the C2-C3 axis. Of course, you can draw a Newman projection down any bond axis, but the C2-C3 axis is the most beneficial to view in a Newman projection.

 

Below are some more questions to help you practice this.

 

Problem #2: Do you understand relative energies? Which are the lowest and highest energy confirmations of a Newman projection?

        

If we take what we learned above, with respect to how to draw a Newman structure and the types of conformations that exist, this problem becomes much easier. For the purposes of undergraduate organic chemistry, 98% of the time the lowest energy structure is going to be a staggered structure where the largest groups are 180 degrees away from each other. This is the lowest energy conformation because there is limited torsional and steric strain. We will go into torsional and steric strain more below. Try these practice problems to see if you can come up with the lowest energy conformation of these Newman projections.

 

Problem #3: Do you understand strain? Is there torsional or steric strain?

           

 

There are two types of strain that can be seen using a Newman projection. The first is steric strain. This is much more common in other types of organic chemistry problems, and occurs when two large groups are near each other. With respect to Newman projections, anytime two groups that are a methyl size or larger are near each other there is steric strain. Hydrogen-hydrogen interactions do not really lead to steric strain like a methyl-methyl interaction will.

 

The second type of strain is torsional strain, which occurs when bonds overlap. For the purposes of Newman projections, anytime we have an eclipse conformation there will be some torsional strain. Armed with this knowledge, let’s look at some more problems.

 

Practice problem #4:  Do you understand relative energies? Draw the energy diagram for a Newman projection:

 

Energy diagrams show the relative energy of a molecule compared to rotation about the axis of interest. Generally, these start at 0 degrees and rotate through the entire molecule. This can then be graphed showing which parts and bond angles about the axis of interest are more or less stable. Because this diagram is relative, we will make some educated guesses when we draw it out. To make one of these energy diagrams, we have to have a good idea ahead of time of what the lowest and highest energy conformations are. To do it thoroughly we are going to walk through the conformation and check the relative energy every 60°. Since there are 360 degrees in a full rotation, that means we will have six different energy points to plot on our diagram per molecule. Here is a good example of what one of those will look like.

Newman projection practice problems #5: What about advanced Newman projections? Draw cyclohexane as a Newman projection.

 

Students should realize the Newman projections are not just confined to linear molecules. Newman projections can be used in cyclic molecules also. Some professors like to test this concept using cyclohexane. With a little bit of practice, this can be done relatively simply. The main thing to remember is that in cyclohexane’s Newman projection there are two axes of interest.

 

 

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5 Cardinal Rules of Carbon in Organic Chemistry

 

If you haven’t noticed by now, carbon is the most important atom in the organic chemistry world. It is all about carbon chemistry.

 

 

 

Here’s a hint: if it doesn’t have carbon in it, it is most likely not an organic molecule. Carbon is the basis of everything in this class. In some cases carbon will be a nucleophile, and in others it will be an electrophile. If you’re just starting out, there are some things you should know about carbon that will make your life a lot easier through your organic chemistry class.

 

  1. Carbon is the most important atom in the organic chemistry world.  I think we have sufficiently emphasized this point now.

 

  1. The sp3 carbon atom is a tetrahedral molecule with bond angles at exactly 109.5 degrees.

 

  1. Carbon atoms can be hybridized in three separate ways. sp, sp2 and sp3. sp3 hybridized carbons are seen in alkanes. sp2 hybridized carbons are seen in alkenes, and sp hybridized carbons are seen in alkynes. See below for a good picture of the bond angles for each.

 

 

 

  1. Carbon usually has four bonds to it. It can sometimes have three bond, and in rare circumstances even have two bonds. It will never never never never never have 5 bonds. Did I say never enough times? Seriously, don’t ever put 5 bonds to carbon please.

 

 

  1. Chains of carbon are called hydrocarbons and really only do two things. They are solvents, and they can be burned. That’s really about it.  This is because there is not a huge difference in electronegativity between carbon and hydrogen. Therefore it is not a polar bond, which means it doesn’t have polarized electrons which facilitate chemical reactions. This makes hydrocarbons very boring and non-reactive. Nonpolar, boring nonreactive molecules are great nonpolar solvents. But other than that they really don’t do much. There are ways to activate the C-H bond to do chemistry, but most of those are beyond the scope of undergraduate organic chemistry.  The exception is free radical halogenation of an alkane.

 

We are huge fans of molecular modeling kits to help you visualize the carbon atom and other atoms you will see in this class. Here is our favorite molecular modeling kit, which we just happened to create. It comes with a DVD which has two hours of instructional videos on it.

 

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5 things you need to do to succeed in your organic chemistry class

How to Succeed in Organic Chemistry

 

Welcome back.  If this is the beginning of your organic chemistry experience, congratulations.  Most student take organic chemistry because they want to go to medical school, because it is a requirement for their degree in a science, or because they are interested in the topic.  (By the way, the last group of students is by far the smallest).  Whichever group you are in, organic chemistry can be an exciting, fast paced, wild ride.  OK, it is not an attraction at Six Flags, but it can be interesting and challenging, depending on your instructor.

 

However, lets get to the meat of this post.  How do we study for this course?  Here is our official five-step guide for how to study for organic chemistry.

 

Step 1: Keep calm and just study.  Nobody but the gifted and boring can get an A in organic chemistry without studying.  Gosh darn it, you have to commit to this class if you want a good grade.  That doesn’t mean that you need to freak out over it, but you will need to bear down and take this monster seriously.

 

Step 2: Learn the language.  Organic chem is a different language for most people.  Literally.  And if you don’t know that language or are slow in its translation, you will be behind everyone else who is fluent.  Think about it this way: If your professor rattles off a long thought and uses a lot of organic terminology, how long would it take you to decipher it?  Might the professor already have moved  on to the next thought by the time you have decoded the previous one?  Make sure you know the language so you can learn the skills.

 

Step 3: Know the easy reactions cold.  What are the easy reactions?  E1, E2, SN1, SN2, and alkene reactions are the first places that you need to start without even thinking about it.  Don’t waste time on an exam struggling through the easy reactions.

 

free organic chem study guide

 

Step 4: Learn the basic premise of organic chemistry mechanisms, which is that electrons always flow from nucleophile to electrophile.  If you can identify which is the nucleophilic site and which is the electrophilic site, you will be well on your way to figuring out the answer to that problem.

 

 

Step 5: Do 50 billion practice problems.  And once you have done that many, try to get to 60 billion.  Do all of the problems in your textbook.  Buy or make your own flashcards.  You cannot do too many of these.  Not only will it help you to learn how to do the problems, it will also help ensure that you are not surprised by a problem you have not seen before.

 

So that is it.  Five simple steps to a good grade in organic chemistry.  Do you have anything to add to the list?  What has been helpful for you?  Email us at admin@aceorganicchem.com and tell us what works for you.

 

 

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We asked professors about the best way to study organic chemistry

So it took over two years to complete, but we surveyed a bunch of organic chemistry professors and asked them ten questions about the best way to study organic chemistry.

The results were a little surprising to us.  So we compiled all of the results into one webpage and made it available to everyone.

See it here: Best way to study organic chemistry.

Basically, organic chemistry does not have to be hard.  If you study the right way and work hard, you can do this.

Check out the results of the survey at the link above.

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Large-Scale liquid manufacturing

I recently ran across eliquidwholesaleusa.com. I found the site really interesting, from a chemistry point of view. They are an insured wholesale e-liquid manufacture. They offer such services as custom private labels, wholesale supplier services, and an ISO-7 clean room for manufacture, which is coming soon. They are special for number of reasons. They have a lengthy history in the industry, all of their products are insured, they are dedicated to quality control, and they have some of the lowest cost in the industry.

I think they are especially good for the new upcoming business who wants to wholesale their products, but doesn’t really know where to start. Their customer service is pretty good, so they will be able to start you off on the right foot. Furthermore, they do private labeling, which is really cool for the start-up company that wants their own label and branding. You can explore the limitless possibilities by starting with your own manufacturing label using this site.

Their production facility is really unmatched in this space. They take it personally upon themselves to make the highest quality liquids, and customer satisfaction is their number one goal. They own a 10,000 square-foot facility allowing them to produce nearly 1,000,000 bottles a month. Everything is manufactured in a free and clean space to preclude contamination. They have the highest standards of manufacturing to make sure that they provide a safe and satisfactory product for their clients. Their industry knowledge is unmatched, they have competitive pricing, and a widely customizable product.

If you are interested in starting your own e-liquid private label or are just curious about the chemistry that goes along with a manufacturing facility like this, I suggest you check out their site. They are only a click away and you can pick up some pretty good information on industrial chemistry.

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I am a Chem Major….what about jobs after school? Part 1

So, the most recent questions I have received is about chemistry majors getting a job.

Specifically: 1) What type of jobs are out there and how do they pay?  2) do I need a graduate degree?  and 3) are they dangerous?  Today, we are going to answer question 1.

First, there are a vast number of jobs available to someone with a BS in chemistry.  In fact as recently as 2007, there were 110 jobs right now for every 100 graduates.  Even with the economy slowing and the uncertainty of the situation in Washington, the industry is still hiring in healthy numbers.

There are a wide range of jobs that someone with a chemistry degree could apply for.  The most obvious are in the pharmaceutical industry.  While in some jobs you may just be a pair of hands running experiments for someone else if you have a BS, the job can still be challenging.  Further, BS chemists have the most room in a company to grow.  PhD chemists suffer in industry because there  is only so high they can go in management without a business degree.  BS chemists on the other hand can advance, get raises and even go into supervisory roles without an advanced degree.  Moreover, BS chemists are highly competitive to get into most graduate schools if they have a few years of experience in the pharmaceutical industry.

Pay and benefits are “Big Pharma” are great too.  The average pay for a BS chemist with over 20 years of experience is well over $100K, according to the most recent ACS employment survey of chemists.  Starting salaries are very good, with young BS chemists starting around $65-70K.

Overall, the whole thing just makes sense.  From personal experience, I would highly recommend this job to anyone who is interested in chemistry or even the sciences in general.

Hope that helps.  Good luck with finals and keep a chemistry major in mind for the future.

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86 Tricks To Ace Organic Chemistry – Multimedia Edition is now available for the iPad

AceOrganicChem.com is very proud to announce the release of it’s best-selling book, 86 Tricks To Ace Organic Chemistry, as an iPad multimedia book. In addition to the material that made the previous version a must-read, it now also contains videos, flash cards and practice problems, making it an instant hit. It is quite a wonder and a must see on the iPad.

http://itunes.apple.com/us/book/organic-chemistry-86-tricks/id507347523?mt=11&ls=1

Now available in the iBookstore for only $7.99, it really is something to see.

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