Archive for the "Organic Chemistry General" Category

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!

Summer Organic Chemistry Studying Tips

Posted on June 11th, 2016

Many students take Organic chemistry in the summer because the curriculum is cut in half.  You have only 8 weeks instead of 16 and the material is covered much more quickly.  This can be a great time-saver for your academic calendar, but it makes your studying twice as more challenging!  This class will be very fast paced, anywhere between 50-100 reactions will be presented, and the organized student will be the only one to get a great grade in the class. Fortunately, we here at StudyOrgo have developed simple, clear-cut explanations to help simplify your studying and maximize your time. Follow these tips for studying this semester and sign up with StudyOrgo today to help you get all of your reactions mechanisms and descriptions instantly!

  • Read ahead – You only have 8 weeks for this class, so staying up on the material is absolutely the most important thing to do!! Read two chapters this week to catch up and get yourself ahead of the class.  Don’t try to understand everything, just read the text and try to understand the big ideas. After you have read the chapter on the material for the next lecture, you’ll find it will completely change the way you pay attention in class.  You will pay more attention and come up with questions about the details of the material that are tricky, rather than scrambling to write down notes and drawings.

 

  • Attempt ALL homework problems – Students, who pay hundreds of dollars for a single tutoring session, 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 couldn’t agree more!  Practicing the problems will make it easier for the quizzes and tests.  We have even developed a Quiz Mode that each student can customize to their studying needs.  Our presentation also allow for Flash Card mode, which allows you to quiz yourself as you study!

 

  • Read everything listed on the 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 how you will be graded. Professors 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! –Another useful tip that past students have succeeded with is to take a calendar and divide the time you have until the next test by the number of chapters. Schedule 2-3 hours a week AT LEAST to study and DON’T SKIP OR RESCHEDULE. Use your iCal, Outlook or other smartphone calendar to send youself alerts and reminders for your studying appointment.

 

  • Sign up with StudyOrgo – The content of a StudyOrgo.com membership includes 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) which 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 WILL get a top grade in your summer Organic Chemistry course.  Sign up today!!

Molecular Orbital Theory

Posted on June 5th, 2016

One of the most challenging concepts in conjugated system reactions is molecular orbital interactions, or MO theory.  The basics to this principle can be hard to grasp, but will be very informative in predicting the correct reaction conditions and outcome of the reaction if you understand them, which will give you a major advantage on future quizzes and exams.  We at StudyOrgo have devised a simple explanation of the basics to MO theory to help you with your study preparations.

Principles of MO Theory

The basic concept of MO theory is to describe the alternating patterns of orbitals that exist in pi bond systems.  We describe the orientation of each half of the dumbbell orbital centered around an atom as being bold or open. Remember, there are bonding and antibonding orbitals.  Essentially, orbitals with lower numbers of nodes (switches in the orientation of the dumbbell orbital which we show with the dashed line) behave more like bonding orbitals while orbitals with higher numbers of nodes behave like anti-bonding orbitals.  To determine what orbitals are occupied on your molecule, simply count how many pi bonds you have in your conjugated system.  Below is an example of butadiene.  It has 4 pi electrons, so we fill the lowest molecular orbitals first, two in each orbital.  Therefore, the highest occupied molecular orbital, or HOMO, in butadiene is #2.  As a result, the lowest unoccupied molecular obital, or LUMO, in butadiene is #3.  We can extend this to ethylene and see that with 2 pi electrons, molecular orbital #1 is the HOMO and molecular orbital #2 is the LUMO.

MO #1

Cycloadditions MO Theory

Remember that cycloaddition reactions describe the formation of new C-C sigma bonds through rearrangement of the pi electrons in a conjugated system.  Therefore, we need to use the molecular orbitals of the pi electrons to drive the reaction.  Let’s take the reaction of butadiene with ethylene, the most simplistic Diels Alder reaction (4+2 cycloaddition).  We start with the most conjugated molecule, butadiene and examine its HOMO.  Then we look at the least conjugated molecule, ethylene and examine its LUMO.  Why?  We need the electrons from a HOMO to flow from one molecule to another, so we have to use the LUMO orbital that is not occupied for this process.  We see that nodes of the HOMO and LUMO align; that is the open and closed halves of the dumbbells align.  This leads to a forward reaction and formation of the product, cyclohexene.

MO #2

However, in another example where we have a (2+2 cycloaddition), we see the HOMO and LUMO of ethylene do not align thus forbidding the reaction.  However, we have the ability to excite electrons from the HOMO to a higher orbital using light (hv) or heat, thus changing the HOMO.  We review this concept in detail in a previous article. When we do this, the HOMO of excited ethylene and LUMO of ground-state ethylene align and the reaction produces cyclobutane.

MO #3

We hope this description has helped clarify this concepts of MO theory. This is an example of the clear and simple expatiations we have prepared for over 175 reactions commonly seen in Orgo1 and Orgo2 courses.  Sign up today for your study preparation needs!

Tips on Sigmatropic and Electrocyclic Reactions

Posted on May 18th, 2016

One of the most common difficulties in Orgo 2 is the concept of sigmatropic and electrocyclic reactions.  Both of these reactions involve conjugated pi bond systems, which are multiple, adjacent carbon atoms with connected pi bond orbitals.  The Greek word sigmatropic literally means “sigma(bond) changing”, thus when presented with a conjugated pi bond molecule where bonds are broken and formed, the driving force of this reaction is carried out by moving the pi-bond system around the molecule.  Two types of sigmatropic reactions are common for this class.  First is the Cope rearrangement.  This is also referred to as a [3,3] sigmatropic rearrangement.  Many students struggle with with nomenclature, especially since the [x,x] nomenclature is most often presented on tests.  What does it exactly does [3,3] or [1,5] mean?

Lets look at a few examples.  Below is a typical Cope Rearrangement with [3,3] sigmatropic rearrangement.  We see that the reactant has 2 pi bond (or 4 pi electrons) in a pseudo-cyclic arrangement. Right now, each alkene has one substituent that is not an H.  if we move the pi-electrons around the ring, we can form a resonance structure (middle molecule) which is a complete ring.  The product is to break the sigma bond in red and form a sigma bond in green.  But why are there three arrows (meaning 6 electrons) involved in the mechanism?  This is because while in the reactant the red bond electrons are sigma, when the molecule rearranges, they will be used to form a new pi bond, while the reactant pi bonds will donate electrons to become the green sigma bond. Now one of the alkenes has two substituents, which is more favorable and drives the reaction to the right.

A question that comes up frequently is what the numbering of the rearrangement means?  To determine this, there a few easy steps to follow;

  1. Identify what bond will break and what bond will form.
  2. Draw an imaginary plane that intersects these two bonds.
  3. Count the atoms starting from the top of the plane from where the bond was broke to where it forms. This is the first number [3.x]
  4. Count the atoms starting from the bottom of the plane from where the bond was broke to where it forms.  This is the second number [x.3]
  5. Placing them together, we can see that a [3,3] sigmatropic rearrangement means a new bond is formed between atom 3 above and atom 3 below the imaginary plane.

The same is true for non-carbon atoms in the ring.  The second example looks at a [1,5] sigmatropic rearrangement of hydrogen (also called [1,5] hydride shift).

  1. Identify what bond will break and what bond will form.
  2. Draw an imaginary plane that intersects these two bonds.
  3. Count the atoms starting from the top of the plane from where the bond was broke to where it forms. In this case, there is only one atom, the hydrogen.  This is the first number [1.x]
  4. Count the atoms starting from the bottom of the plane from where the bond was broke to where it forms.  This is the second number [x.5]
  5. Placing them together, we can see that a [1,5] sigmatropic rearrangement means a new bond is formed between atom 1 above and atom 5 below the imaginary plane.

sigmatropic article 1

In cases where oxygen is present as an ether, the name of the reaction is changed to Claisen Rearrangement.  However, the mechanism is the same.  The aldehyde or ketone product is almost alway preferred to the ether reactant shown here.

sigmatropic article 2

 

Another question that is typically a major stumbling block of students is the rules for choosing reaction conditions for electrocyclic reactions.  This refers to the rotation of pi bonds  to form new sigma bonds or the rotation of sigma bonds to form new pi bonds.  The two atoms can rotate their orbitals in such a way that they rotate in the same directions (conrotory), which gives trans- orientation, or in opposite directions (disrotory), which gives cis- orientation.  The main point is that the substituents on the these atoms will be in different stereochemical arrangements.  When a chemist wants to choose the correct stereochemical outcome of the molecule, you have to choose the right conditions to get the substituents of these electrocyclic atoms in cis- or trans- to each other.

 

Below is a convenient table to help you identify the right condition for the reaction presented to you.

electrocyclic

 

 

How to approach synthesis problems

Posted on February 9th, 2016

Q: “I am in organic chemistry 2 and I am trying to learn how to predict the products.”

One of the most challenging, but ultimately the main goal, of organic chemistry is to take an abundant, cheap starting reactants and transform it into a biologically active or synthetically useful product.  In the two semesters of organic chemistry, you will learn reactions that will produce all of the functional groups that give molecules these useful properties. But as a chemist, it is very importantly to accurately predict how and in what yield these reactions will produce you desired products.

The stakes seem higher when you are given less than 2 hours to complete several multi-step synthesis problems that often ask to identify not only reagents but the mechanism of each step of the reaction.  We here at StudyOrgo have compiled advice and guidance for learning to tackle these problems.

  1. Relax!
  2. Understand that each step in a synthesis reactions can be broken down into two basic types of reactions;
    1. Change in the carbon-carbon skeleton: Take a look at the starting material and the final product. Count the carbons, is there a difference in number?  If so, then you will need a carbon-carbon bond breaking or addition reaction.  There are only a few examples of these reactions so that instantly narrows down reactions you have to focus on.
    2. Change in the identity or location of a functional group: This is the most common synthesis question. Remember, that the pathways from one functional group to another are limited.  Set up a reaction roadmap or use included with your StudyOrgo membership to help you memorize what reactions can be used to get you to your final functional group.
  3. There are often times MANY routes to get to a final product. ALL OF THEM ARE CORRECT, if in fact the route is possible.
    1. HINT: Professors will only ask you to use reactions they have covered in class. Make a list and indicate what the reaction does to help you memorize the products.
  4. Sound out the problem. Often time students have a viable synthesis approach, but get held up at one or two places and just leave the entire question blank. Remember, it is multistep, which means there are many places to get points!  Draw out what you know.  Worst-case scenario: you get partial credit.  Best case scenario: you realize what reaction is next and get full points!!
  5. Practice, practice, practice! Make sure to perform all of your practice problems assigned to you for each chapter.  It takes a lot of time and effort, but likely these examples will be used by your professor.  Also, the more examples you see the less surprises will be on the exam!
  6. Sign up with StudyOrgo for help! The Editors at StudyOrgo have spent numerous hours reviewing and preparing the material in the most crystal-clear and “get-to-the-point” manner as possible. We provide quick descriptions and in-depth mechanism explanations. 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!