Archive for the "Organic Chemistry General" Category

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!

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Reviewing Molecular Orbitals

Posted on August 16th, 2016

Gearing up for Organic Chemistry this Fall semester is a smart and efficient way for reaching and maintaining a great grade in this class.  Most students find the pace of this class very accelerated compared to other courses.  This is because while there is a lot of information to learn, it also builds on previous concepts from general chemistry, a course most students want to forget!

But don’t worry!  StudyOrgo has you covered.  Our Editors have spent years tutoring and teaching Organic Chemistry to students and we have seen all of the pitfalls common to the first few weeks of the semester.  Our online platform allows members to learn organic chemistry concepts and mechanisms quickly and the material presented in an easy-to-follow format. Follow along with us and sign up with StudyOrgo today to help prepare you for all of your Organic Chemistry questions.

One of the concepts you will need to have mastered before you  begin the class is Hybridized Orbital Theory.

Lets look at carbon, the atom this class is about.  Recall that it has atomic number 6, which means it has 6 electrons.  Remember that the rows, or periods, of the periodic table reflect the outer electron orbital.  In the second period, carbon has 4 electrons in its outer orbital.  These are the electrons that are available for bonding.  The carbon atom wants to eventually achieve 8 electrons to fulfill the Octet Rule, so it needs to make 4 covalent bonds. Below is how the electrons are filled in their orbitals.  Recall that the columns, or groups, of the periodic table reflect the type of electron orbitals present in the atom.  The red block is the location of carbon, which indicates that carbon has 2 s-orbital and 2 p-orbital electrons.

AO fig 1

These electrons are arranged in an energy diagram according to their energy, shown below

AO fig 2

But it we consider the molecular shape of methane (CH4), we will observe it as tetrahedral, where all 4 C-H bonds appear to be equal, so how do the electron energies become equal?

 

Picture1

We explain this observation by assuming that the s-orbital and p-orbital electron energies, while different merge into an sp3 hybridized orbital.  In this model, the 2 s-orbial and 2 p-orbital electrons merge into something that resembles a dumbbell.  Since all of the orbitals have the same shape and energy, the C-H bonds of methane can be equal and form the observed tetrahedral orientation.  There are three types of hybridized orbitals for carbon;

AO fig 4

  • sp3 – which has 4 single (sigma) bonds. The molecular geometry is tetrahedral.
  • sp2 – which has 3 single (sigma) bonds and 1 double (1 pi) bond. The molecular geometry is trigonal planar.
  • sp – which has 2 single (sigma) bonds and 1 triple (2 pi) bonds. The molecular geometry is linear.

With a good study plan and help from StudyOrgo, you’ll have no trouble passing your organic chemistry quizzes and exams this semester.  Sign up today for more comprehensive and clear-cut explanations on all of your organic chemistry topics today!

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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!

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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!!

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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!

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