Archive for the "Organic Chemistry General" Category

Question from one of our students: Is there any way to practice the mechanisms of the various organic reactions on this program?

Answer from one of our StudyOrgo.com Experts: Thank you for your inquiry. Yes, our program highlights the key points about mechanisms in the reaction description sections of the flashcards. These are written under the heading of “Mechanism Hint.” Additionally, the full mechanisms for the reactions of SN1, SN2, E1, E2 can be found in the dedicated StudyChart: “SN1 SN2 E1 E2 Comparison Chart.” We do not write out the entire mechanism for each reaction because this information can be easily obtained in any standard organic chemistry textbook. Our materials present key tips, tricks and hints that textbooks and professors don’t tell you but can be very valuable for exams. Additionally, mechanisms are typically a small portion of any classroom exam and it would typically inefficient to try to memorize every single mechanism. Rather, you may want to learn the ones that your professor highlights. Our materials will help you understand the reactions and other topics that will be tested in a very thorough manner. Take time to learn each reaction in Study Mode, then practice what you learned by creating custom quizzes in our Quiz Mode. If you every have any questions, please do not hesitate to contact us at any time.

This question from one of our Twitter followers:

Answer from one of our StudyOrgo.com Experts:

That is a great question. Cyclopentyne is an extremely unstable molecule. Cyclopentyne has two main inherently unstable properties:

1. it is a small membered ring structure
2. is has a triple bond in the molecule

Let me explain each of these:

#1- it is a small membered ring structure
The smaller the carbon ring the more unstable it is. The reason for this is that the molecule cannot freely rotate about each bond. This is referred to as ring strain. The smallest carbon membered ring is cyclopropane which only has three carbons. This molecule has the highest ring strain of all the carbon rings. A five membered ring such as cyclopentyne is not too far from that.

#2- it has a triple bond in the molecule
The triple bond within the molecule is an example of sp hybridiation. You may recall that this geometry assumes a bond angle of 180 degrees. However when you force a triple bond into a ringed structure such as cyclopentyne, you are forcing the hybridization to assume a bond angle less than its preferred orientation of 180 degrees where the normal bond angle in such a structure is 108 degrees. That’s certainly much less than 180 degrees and that makes that carbon to carbon bond very unhappy!!

So, if the issue of ring strain wasn’t enough, now add on top of that an sp hybridized carbon to carbon interaction of the triple bond forced into a much smaller bong angle than it is accustomed to and you are left with a very unstable molecule. For these reasons no one has ever been able to make cyclopentyne as a stable molecule.

Do you need to know Organic Chemistry to be a great doctor?

No. But Medical School Admissions Committees sure do think so. It is well known that Medical Schools look closely at your Orgo grades from college when they consider you for admissions to their school. This is true. Let us explain.

Medical Schools like to see that an undergraduate student has excelled in Organic Chemistry. Some say it is because Organic Chemistry is a difficult subject and can help differentiate among those students who are stronger than others. Others say it is highly applicable to a typical medical school curriculum and thus those who have excelled in organic chemistry as an undergraduate are more likely to excel as a medical student. The bottom line is that for whatever reason, Organic Chemistry courses seem to produce a greater distribution of grades than do other pre-med courses such as Biology or General Chemistry. Therefore Medical School committees can use this to their advantage and thus can “weed” out weaker students. Are those students truly weak? Probably not. However when admissions committees need to review thousands of applications and can only accept a hundred or so students, they look for any possible way to dwindle down their heaping piles of applications.

Here are some other trends that committees tend to look for:

1) Good grades in both Orgo I and Orgo II

2) Improvement from Orgo I to Orgo II

3) Good grades in Organic Chemistry Lab

4) Good subject score on the MCAT Biologic Sciences demonstrates excellence in Organic Chemistry.

5) Strong letter of recommendation from an Organic Chemistry Professor (if applicable)

For these reasons, we feel it is important to concentrate while taking Organic Chemistry. Here are some tips:

1) Try to take and complete General Chemistry prior to taking Organic Chemistry

2) If possible, try to have a lighter course-load during the semesters that you take Organic Chemistry.

3) Scope out which professors teach the course you are looking to take depending on the time of the year. Some professors are “known” to be “easier” than others. Should it help to take Orgo I in the Spring and Orgo II in the fall, do so.

4) Obtain your resources early.

5) Develop a study plan and stay ahead of everyone else.

6) If you see that you are having trouble, try to identify so as early as possible.

7) Try to figure out what you professor places an emphasis on. That is what is more likely to be tested on your exams.

8) Ask your professor for old exams to get practice.

We here at StudyOrgo.com are aware of this. Therefore we have designed out study tools to combat the typical traps that students fall into. In addition, we highlight the common subjects that students have trouble with so as to separate you from all the rest of the class and get an edge on the competition.

So what are you waiting for? Sign-Up and begin acing Organic Chemistry today!

Question from one of our Twitter followers:

“While naming a complex organic compound, the substituent is ordered in which manner? The numbering.”

Answer from one of our StudyOrgo.com Experts:

Find the longest chain of carbons in the molecule and number them starting with the carbon closest to a branch.

Note: If there is a branch at the same point at either end, start numbering at the end closest to the largest branch. If the branches are of equal size at the same point at either end, start numbering at the end where the next branch is closer.

For access to our simple step-by step guide to naming in orgo and our exercises on this topic, sign-up for an account then visit Part 5 of our Summary Guide.

Question from one of our Twitter followers:

“How to calculate the no.of non-bonding e- around “a” atom.& how to make sure whether the organic substance is major or minor”

Answer from one of our StudyOrgo.com Experts:

I think what you are asking about two things: how to draw a Lewis structure and how to determine which resonance structures are major and which are minor contributors.

First I will address the Lewis structure:

A Lewis structure is a way to draw out electrons and bonding by using dots. In a Lewis structure some of the electrons are “bonding electrons” and others are “non-bonding electrons” known as “lone pairs.” Here is a simple step by step process using CO2 as an example:

1. Step 1: Determine the number of valence electrons an atom has to participate in bonding.
   1. Definition: Valence electrons are the electrons in the outermost shell of an atom. Some valence electrons participate in bonding to another atom. Others, known as lone pairs, do not.
   2. The number of valence electrons that participate in bonding for popular atoms are as follows:
      • C = 4
      • N = 3
      • O = 2
      • F = 1
      • H = 1
   3. For example: In CO2 we have C (draw 4 dots) and O (draw 2 dots per atom)
2. Step 2: Place a dot around that atom for each valence electron that participate in bonding
   1. For example:  
3. Step 3: Determine the lone pairs for a given atom:
   1. Remember: Lone pairs are a subset of the valence electrons that do not participate in bonding to another atom
   2. Lone pairs for popular atoms are as follows:
      1. C = 0
      2. N = 1 pair = 2 electrons
      3. O = 2 pairs = 4 electrons
      4. F = 3 pairs = 6 electrons
      5. H = 0
   3. For example, in CO2 we have C (no lone pairs) and O (two lone pairs per atom)
4. Step 4: Place the lone pairs around the atom using a pair of dots to depict each lone pair.
   1. For example:
      1. 
5. Step 5: Wherever there is an atom bonding to another atom there are two dots between them, one from each atom. You may decide to convert this pair of electrons into a line to denote a bond.
   1. For example: 
6. How do I figure out an atom’s formal charge?
   1. Step 1: Count the atom’s lone pair electrons
   2. Step 2: Count one from each pair of electrons that particular atom is using to bond to another atom
   3. Step 3: Add the number you get from Step 1 to Step 2
   4. Step 4: The formal charge is whatever you need to do to the number you got from step 3 to get to the atom’s group number on the periodic table
   5. For example: Let’s use an O atom in CO2 as an example

Add the lone pair electrons (4) to one from each pair of bonding electrons (2) = 6

Since oxygen is in group 6 in the periodic table the formal charge is 0 (zero). (You do not need to do anything to the number you get from step 3 to get to the atom’s group number on the periodic table)

Next I will address the Resonance Structures:

1. A drawn structure with a double bond on its own does not completely represent the structure of a given molecule
   1. There can be more than one possible structure for the same molecule!
   2. The actual structure is the average of all of the resonance structures

• Why resonance?

1. Resonance spreads the charge over two atoms which makes the structure more stable

• How do I figure out resonance problems? Follow these simple rules:

1. Rule #1: Try moving around electrons.
   1. When moving electrons use an arrow to demonstrate where the electrons are going.

• Electrons can be moved around in one of two ways:

1. Move double bond electrons
2. Move lone pair electrons

1. Rule #2: The number of unpaired electrons must remain the same
2. Rule #3: Figure out which of your drawings represent the major and minor structures
   1. Major resonance = the resonance contributors that are more stable as they have the least energy. Low energy structures satisfy as many of the following as possible:
      1. There are as many octets as possible
      2. There are as many bonds as possible
      3. There are as few lone pairs as possible
      4. Any negative charges are placed on the most electronegative atoms
         1. Most electronegative F > O > Cl > N > C least electronegative
      5. There is the least separation of charge amongst the structures
   2. Minor resonance = the resonance contributors that are less stable as they have the most energy. High energy structures do not satisfy as many of the above guidelines
3. Example: NO3-
   1. In the following example NO3- is drawn out showing three different resonance structures. Please remember that while electrons are moving around no atoms are moving.
   2. The arrows show the movement of the electrons to show how to arrive at the next structure moving from the left to the right of the screen.
   3. Since all three structures satisfy the same guidelines to the same extent as outlined above, all three are equal contributors. However this is often not the case and will be seen in the next exercise set.