Archive for the "Organic Chemistry Reactions" Category

Organic Chemistry Reactions blog archives will get you quick tips on organic chemistry reactions for your examinations ahead. Organic chemistry reactions were never easy before StudyOrgo.com came online.

Learning Reactions FAST!

Posted on October 26th, 2016

 

Learning organic chemistry is a very challenging for any undergraduate student, however it is a prerequisite course to many advanced degrees and necessary first step to understanding the reasons for how disease originates and how pharmaceuticals are designed to alleviate symptoms and cure disease.

One of the questions we receive at StudyOrgo frequently is “how do I learn reactions fast?”  The answer is different for each student and will require a lot of practice and patience on each student’s part, but we here at StudyOrgo have devised clear-cut and refined illustrations of over 180 examples of reactions commonly covered in the two semesters of organic chemistry.

To help you study gear up for your Fall Semester studying, we have outlined here some tips for studying organic chemistry reaction mechanisms quickly and efficiently.

Learn the basics of each reaction class mechanism: In this class, you will learn that the “flow of electrons” drives the mechanisms for every organic chemistry reaction. Understanding how electrons flow using specific functional groups is essentially all you are learning in this class!  Take for instance reactions of ketones.  Nucleophilic attack by hydride (H-) on the ketone carbonyl to form an alcohol uses the same mechanism as nucleophilic attack by H2O to form a diol, however the products are different because of the characteristics of the reagents.

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Assemble a “road map” of reactions in the same class: Once you learn how electrons “flow”, all you need to do is memorize the reagents and what the produce! Tables work for some students, however StudyOrgo has come up with an interactive “Reaction Road Map” to help you trace what functional groups are interchangeable by using specific reagents.  This can greatly speed up your memorization of organic chemistry reactions!

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Quiz you self with as many homework and sample problems as possible. StudyOrgo as developed a comprehensive set of over 180 reactions you will see in organic chemistry 1 and 2. We devised an innovative approach to integrate our extensive website content into the ability to aid fast studying of mechanisms into a Study Mode and Quiz Mode.

In Study Mode, all of the information is presented to you in a clear-cut format.  Reagents and products are presented the the left and right of the arrow.  Above the arrow, reagent that are necessary for the reaction are presented.  Below, Benny’s notes are listed to give you the tips and tricks of every reaction presented!  Very handy for learning the difficult or complex mechanisms!  Finally, the complete step-by-step mechanims with arrows, intermediates and transition states are depicted.  Several examples of each reaction are also illustrated in the website.  Use Study Mode to help you master these reactions fast, without paging through you notes or the book!

study-mode

In Quiz Mode, you have the option to select any functional groups and add them to your custom quiz.  You can decide if you want reactants, reagents and products all covered up or just certain parts.  You can even select them to be randomized or in order, you can also choose how many questions you want asked!  Then save the quiz and take it!
quiz-mode

You will see reagents and products are “covered up” to aid you in flash-card style studying of the material.  The “scratch pad” below the question will be useful for predicting what the answers will be. You can customize the Quiz Mode to cover some part or all parts of the reaction based on what you would like to quiz yourself on.  For example, if you professor says you are responsible for the reagents but not the mechanism, select reagents in Quiz Mode and only reagents will be hidden. This will help you to identify a reagent functional group transformation based on reagent choice.

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Study every chance you get. StudyOrgo has developed an iOS and Android compatible app to help you with your studying needs!  With you membership, all reaction and website content is accebile to you anytime, anywhere!  Even use Study Mode and Quiz Mode with the app!

 

These are a few suggestions to making organic reaction memorization and as quick and painless as possible!  Sign up today to give it a try!

Carboxylic Acids and their Derivatives

Posted on April 18th, 2016

Here is a look at a reaction directly from our proven organic chemistry flash card system:

Carboxylic Acids and their Derivatives

Esterification of Acid Chloride

Overall Big Picture: In this reaction, an acid halide is reacted with an alcohol to give an ester.

Acid Chloride + Alcohol → Ester

Key Tip: A mild base is required to drive the reaction forward.

Key Comparison: This reaction is only possible due to the high reactivity of acid halides for nucleophiles, even weak ones like alcohols.

Mechanism Hint: Collapse of the addition intermediate is propagated by deprotonating by pyridine, which helps to drive the reaction forward.

Note: When this reaction is carried out using p-toluensufonyl chloride (tosyl group), this reaction is a good protecting group for alcohols.

First window: acetyl chloride

Middle window: alcohol, pyridine

Last window: methyl ester

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Preparation Tips for Spring Semester Organic Chemistry

Posted on January 17th, 2016

 

Going into the spring semester, you might feel like you know what Orgo 2 will be like.  However, the second semester of organic chemistry has a very fast pace, anywhere between 50-100 reactions will be presented. You’ll be responsible for all of them!  Sign up with StudyOrgo today to help you get all of your reactions mechanisms and descriptions instantly!

  • Read ahead – The first week of Orgo2, read two chapters to get yourself ahead of the class. Don’t try to understand everything, just read the text and try to understand the big ideas. This will completely change the way you pay attention in class and allow you to spend more attention and ask questions about the details in class instead of scrambling to write down notes and drawings.
  • Attempt ALL homework problems – When tutoring students, they are often intimidated when we ask them to try sample problems.  But after a few examples, every student does them better and better with each new problem.  Some students have even made comments such as ‘why didn’t I do this sooner?’  We were at StudyOrgo agree!  It takes a lot of time, but practicing the problems will make it easier for the quizzes and tests.
  • Look at a syllabus – Remember, your syllabus is an official contract between you and the professor. Professors are required to disclose what you are required to learn and what grading rubric will be used. Professors can usually remove requirements (to the delight of the students!) but cannot easily add them. Use this to your advantage! Highlight the contents or reactions of the book that will be required and use this to focus your attention when studying this semester.
  • Schedule your studying! – Now that you know where the book is and a rough idea of what you are responsible for learning from the syllabus, take a calendar and divide the time you have to each test by the number of chapters. Schedule 2-3 hours a week to study and DON’T SKIP OR RESCHEDULE. Use your Smartphone calendar to send you alerts and reminders for your studying appointment.
  • Sign up with StudyOrgo – The Editors at StudyOrgo have compiled detailed mechanisms and description of over 175 reactions in the most crystal-clear and “get-to-the-point” format possible.  Many of our reaction have multiple examples, so you can learn and then quiz yourself in our website! For the student on-the-go, we have also developed a mobile app (iOS and Android) provides all the functionality of the website! All of these benefits are included in your StudyOrgo membership!

With good time management and help from StudyOrgo, you can earn a top grade in your Orgo 2 class this semester!

 

Free Radical Halogenation

Posted on September 22nd, 2015

Another common mechanism that is covered in the first weeks of organic chemistry is the free radical halogenation of alkanes.  This mechanism utilizes the homolytic cleavage (one electron per atom) property of halogens when exposed to heat or ionizing radiation (i.e. hv), which is a popular mechanism for future reactions in the course.  Radical halogens can extract the proton from a C-H bond to produce the corresponding acid and generate a radical carbon center.  In this article we will discuss all of the tips and tricks to getting an ‘A’ on your racical halogenation questions.  Sign up with StudyOrgo today for more in-depth mechanism coverage and answers to all of your organic chemistry questions!

Generating a radical halogen: there are THREE critical steps to free radical reactions.

1) Initiation: The Br2 single bond is broken by high energy ligh (hv) to form radicals placing one electron on each atom.

halogen 1

2) Propagation: (Hint: One radical reacts with a single bond to form another radical, thus propagating the radical species to drive the reaction forward.

  1. a) Radical Br abstracts one hydrogen from a C-H bond in propane to form radical propane and HBr.
    halogen 2
  2. b) Radical propane asbracts one Br from Br2 to form the bromoalkane and radical Br, thus restoring the reactants for another round as shown in step 2a.halogen 3

3) Termination: Any two radicals combine to form a single bond.  These species will be in low abundance. Hint: Radicals are destroyed by combining two radicals to form a single bond.  This eliminates the radical necessary for radical alkane formation (green boxes) as shown in step 2a and ends the reaction.

halogen 4

Regioselectivity: How to determine the major product

Radical bromination will always replace the C-H bond on the MOST substituted carbon center because the stability of the radical intermediate is higher with increasing substituents on the carbon center.

This selectivity is the same, but a weaker consideration, for radical chlorination which obeys Hammond’s Postulate, which says that stability of the radical center is outweighed by the extreme exothermicity of radical chlorination (compared to bromination), thus a mixture of chlorinated products is observed.

halogen 5

Stereoselectivity – How to determine the stereochemistry of carbon centers

Radial intermediates (step 2a product) produce a sp2-like hybridization orbital with the lone electron in the vacant 2p orbital, therfore attack of the radical electron on the C-H bond can take place from either side of the molecule.  The result will always produce a racemic mixture (or equal amount) of the two enantiomers.

halogen 6

 

 

The SN1 Reaction

Posted on September 8th, 2015

Another reaction commonly covered in the first weeks of organic chemistry is the SN1 reaction. The SN1 reaction introduces you to repetitive concepts and rules you will encounter all semester, this time focusing on carbocation formation and reactivity. In this article, we will review the important topics of an SN1 reaction.  Sign up with StudyOrgo today to get detailed reaction mechanisms and explanations to prepare you to ace your next exam!

Alkyl halides as SN1 substrates

One of the most reactive molecules involving substitution reactions via SN1 are 2° and 3° alkyl halides.  However, there are a number of considerations to keep in mind to determine if this mechanism of substitution describes your reaction. First, let’s look at a simple SN1 reaction; a sec-butyl halide (a 2° methyl-ethyl carbon center).

sn1 figure 1

Carbocation formation and stability: Let’s break down the reaction name more simply.  The term SN1 reaction gives you 3 pieces of information, first the ‘S’ indicating ‘substitution’, the ‘N’ denoting the reaction involves a nucleophile and ‘1’ describing the process as unimolecular – meaning only the formation of the reactive substrate intermediate determines the rate of reaction.  This process is referred to as the rate determining step of the reaction, and can be thought of as the ‘bottleneck’ in the reaction. The leaving group will break the bond to carbon and take the electrons for the bond with it forming a carbocation intermediate.  Halogens are good leaving groups because of the inductive effects (or electron withdrawing potential) of the halogen atom and is the characteristic of good leaving groups. Carbocation formation is the first, and rate determining step, in the reaction.

sn1 figure 2

Product formation and racemization: Once the leaving group bond is broken, stability of the carbocation is the factor that determines if this mechanism occurs.  The more substituted the carbon center, i.e. 2° and 3°, the more stabilized the carbocation becomes as the positive charge becomes delocalized to the other carbons. Following formation of the carbocation, it will then react with the nucleophile.  Since the carbocation assumes a planar shape, attack by the nucleophile can occur from either side of the plane.  This leads to formation of a mixture of enantiomers, referred to as a racemic mixture.  This is in contrast to SN2 which will only produce the inverted stereoisomer of the reactant.

sn1 figure 3

Carbocation Rearrangement: As mentioned before, stability of the carbocation is the key step in determining rate and completion of SN1 reactions.  In some instances, the leaving group is bonded to a carbon center than neighbors a more substituted carbon center.  Let’s consider the reaction below, chloride leaves 2-chloro-3-methylpropane to form a 2° carbocation. The neighboring carbon center is 3°, and would make a more stable carbocation.  In this instance, the neighboring hydrogen will shift to the 2° carbocation to form a new 3° carbocation, which is much more stable in a process referred to as a 1,2-hydride shift. Attack of the methanol hydroxyl group on the carbocation followed by proton abstraction by chloride leads to formation of the 3-methoxy-3-methylpropane product.

sn1 figure 4