Posts Tagged "organic chemistry"

Reviewing Acid Base Definitions

Posted on August 31st, 2016

Many students coming into organic chemistry have a difficult time with a concept that was covered extensively in general chemistry but often forgotten over the summer vacation.  This is the definitions of Acids and Bases.  It’s an important part of every mechanism in organic chemistry and your professor will likely assume you are an expert and jump right into the mechanisms whether you are ready or not!

We here at StudyOrgo have countless hours of combined experience tutoring students in just these situations to get you through the material and ready to ace the exam next month!  We have developed comprehensive explanations of the most common mechanisms, but have simplified their explanation in an easy to read format.  We also have developed a mobile app of our entire online content that members will be able to take advantage of while studying on the go!  Sign up with StudyOrgo today for help with Organic Chemistry this Fall Semester!

The classic definition of acids and bases are related to their ability to donate and accept protons into solution.  This is referred to as the Bronsted-Lowry Definition.  However, in organic chemistry, mechanisms are described by the flow of electrons.  Sometimes, an acids and bases can be thought of as their ability to donate and accept electrons.  Therefore, acids and bases were given definitions to reflect this feature.  This is referred to the Lewis Definition.

Type      Bronsted-Lowry Definition          Lewis Definition

Acid       Proton DONOR                                 Electron ACCEPTOR

Base      Proton ACCEPTOR                           Electron DONOR

 

Let’s look at two examples, first using the Bronsted-Lowry Definition.  Reaction of sulfuric acid (H2SO4, the acid) and acetate ion (the base) to produces hydrogen sulfate (HSO4-, conjugate base) and acetic acid (H3O+, conjugate acid).  In this case, sulfuric acid (the acid) donates the red proton to acetate, which can accept the proton with a lone pair of electrons.  Reaction of ammonia (NH3, base) with water (acid) produces hydroxide (OH-, conjugate base) and ammonium ion (NH4+, conjugate acid). In this example, water (the acid) donates the red proton to ammonia, which accepts the proton with one if its lone pare of electrons.

acid base 1

Now let’s look at the same examples, but using the Lewis Definition.  In the sulfuric acid and acetate example, acetate (the base) donates the red pair of ELECTRONS to the red proton on sulfuric acid, which gives the electrons from the green O-H bond back to oxygen to produce the conjugate base, hydrogen sulfate. In the ammonia and water reaction, ammonia (the base) donates the red pair of ELECTRONS to the red proton on water, which gives the electrons from the green O-H bond back to oxygen to produce hydroxide.

Both descriptions produce the same reaction, but are THOUGHT about differently.  In organic chemistry, you will mostly think about DONATING ELECTRONS, because this is what drives a reaction mechanism.

acid base 2

 

We hope you have found these explanations useful and encourage you to sign up today for more clear-cut definitions of many organic chemistry concepts this semester!  Good luck!

What to Expect for Organic Chem Fall Semester

Posted on August 4th, 2016

This semester you will start Organic Chemistry and you have likely heard a lot of rumors about the class; statements from upperclassmen like “it’s difficult”, “this class is impossible” or “the professor is horrible!” We here at StudyOrgo have helped countless students overcome the difficulties of this class and can help you before you even enter the class. We have over 20 years of collective experience tutoring and teaching Organic Chemistry and have developed a few helpful tips that have saved students from the seemingly crushing pressure of Orgo 1.

Hard Organic Chemistry Professor

StudyOrgo has over 180 reaction mechanisms typically covered in Organic chemistry and explained in an intuitive and clear manner available in an online format. We also offer the Quiz Mode to allow you to customize reactions and test your memory of important parts of all of our reactions. We offer simplified and illustrated descriptions of complex concept topics that you will encounter in your first few weeks in Orgo 1. We also have developed a mobile app for iOS and Android smartphones that allows you to study organic chemistry on the go! Sign up with StudyOrgo today to take full advantage of our system!

Here’s what you can expect in the first few weeks of Organic Chemistry 1.

  1. Most professors will spend the first class reintroducing general chemistry topics, but he or she will completely assume you received an A+ in general chemistry and have a full grasp of all these concepts! Refresh your memory of atomic structure, valence electrons, acids/bases and pH/pKa concepts. These will be used right away in Orgo 1. If you aren’t sure, ASK FOR HELP!!

Tip #1 – 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.

  1. Professors will almost always begin quizzing the second week, the midterm is only 7 weeks away. Prepare for them early!!

Tip #2 – Schedule you’re 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.

  1. The class is about to go supersonic speed! Stay ahead of the pace of the class to avoid falling behind!!!

Tip #3 – 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.

Tip #4 – 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.

Most importantly, RELAX!! With a little time management and help from StudyOrgo, you will have no trouble getting an “A” in Organic Chemistry this year!

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!

 

Review of Organic Chemistry 1 Terms

Posted on December 21st, 2015

Many of our students are unclear on a number of key terms that will be necessary to move forward in organic chemistry.  We have compiled a list of commonly misunderstood terms and explain them here.  With this review, our quiz mode review of all of the reactions you have learned and descriptions from StudyOrgo.com, you will be sure to boost your final exam score and get a great grade in your class!

Isomers – There are two types of isomers in organic chemistry.

  • Constitutional isomers – two or more molecules with the same number of atoms but in a different geometrical arrangement (i.e. different connectivity).
  • Stereoisomers – molecules with the same geometrical arrangement (i.e. same connectivity) that are not superimposable on each other. For a carbon center (referred to as a stereocenter), this requires bonding to four different substituents!

chiral 1

  • Enantiomers – A pair of stereoisomers that are mirror images of each other.
  • Diastereomers – Any pairing of stereoisomers that are NOT mirror images of each other.
  • Meso compounds – A molecule with stereocenters that shows symmetry in reflection. Because of this symmetry, the molecule is considered achiral!

Screen Shot 2014-12-18 at 1.00.28 PM

Newman Projections – A way to visualize different rotational conformations of substituent comparing two carbon atoms that looks down their C-C bond, thus showing the alignment of the substituents.

  • Gauche conformation – when the angle between two substituents is 60°
  • Anti conformation – when the angle between two substituents is 180°
  • Eclipsed conformation – when two substituents overlap, or the angle between them is 0°

drawing 6

Stereoselectivity Reaction Terms – describes the reaction conditions that leads to UNEQUAL stereoisomer formation

  • Syn addition – addition of substituents on the same face of the place of symmetry across a double bond.
  • Anti addition – addition of substituents on the opposite face of the plane of symmetry across a double bond.
  • Inversion of configuration – substitution of a nucleophile with the opposite stereochemistry as the starting material (e.g., R ® S). This stereospecificty happens for ALL concerted mechanisms (SN2, E2, etc.)
  • Racemization (racemic mixture) – substitution of a nucleophile which produces both stereoisomers (e.g., R ® R + S). This stereospecificity happens for ALL carbocation (SN1, E1, etc.) intermediates.

 

Regioselectivity Terms – describes the reaction conditions that leads to UNEQUAL constitutional isomer formation.

  • Markovnikov selectivity – in alkene addition reactions, the placement of hydrogen will occur on the LEAST substituted carbon (a.k.a. carbon center greatest number of hydrogens).
  • Anti-Markovnikov selectivity – in alkene addition reactions, the placement of hydrogen will occur on the MOST substituted carbon (a.k.a. carbon center with fewest number of hydrogens).
  • Zaitsev product – in elimination reactions, the formation of the alkene with the MOST substituents is favored. (e.g., E2 elimination with a non-bulky base such as sodium ethoxide).
  • Hoffman product – in elimination reactions, the formation of the alkene with the LEAST substituents is favored. (e.g., E2 elimination with a bulky base, sodium tert-butoxide).

terms figure 2

Intermediate Terms – describes intermediates that are key to reaction progression.

  • Carbocation – formed any time a leaving group breaks a bond with carbon to generate a carbon center with 3 bonds and a positive charge.
  • Oxonium ion – formed any time an alcohol is protonated.
  • Mercurium ion – formed in oxymercuration/demercuration addition reactions
  • Bromonium ion – formed in halogenation addition reactions of alkenes
  • terms figure 3

 

 

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