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1908PharmD

1908PharmD

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This thread will be for any questions that any persons may have about Organic Chemistry :confused::(:oops::):D

Kind of like an online tutor! :idea:
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Can someone please summarize SN1 and SN2 reactions? I have a test tomorrow and he said it will only have SN2 reactions. What are the main ideas i need to know?
 
1908PharmD said:
Can someone please summarize SN1 and SN2 reactions? I have a test tomorrow and he said it will only have SN2 reactions. What are the main ideas i need to know?
Click to expand...

Taken from my notes
conditions for SN1:
*tertiary 3 is highly preferred > secondary 2 > primary 1
*both inverted and attained products are made, but inverted is favored
*stereoselective
*Protic solvents: water, methanol, ethanol, most alcohols
*have carbocation rearrangements

conditions for SN2:
* primary 1 is most preferred > secondary 2 > tertiary 3
* inverted product is the major product
* stereospecific
* Aprotic solvents: DMSO, acetonitrile, DMF
* No carbocation rearrangement

Hope that helps.
 
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1908PharmD said:
Can someone please summarize SN1 and SN2 reactions? I have a test tomorrow and he said it will only have SN2 reactions. What are the main ideas i need to know?
Click to expand...


Hello 1908PharmD...I took organic chemistry 1 spring of last year, so let's see if i can recall as much as possible. Here's a summary of the reactions:

SN1:

- Occurs with secondary and tertiary halides, but the latter halides react the fastest because they form the most stable carbocations. Secondary halides can also undergo SN1 because secondary carbocations are not that
unstable. However, watch out for carbocation REARRANGEMENTS in which a secondary cation is converted into the more stable tertiary cation by a 1,2 methanide or hydride shift.

- SN1 DOES NOT occur with primary or methyl halides because the resulting carbocations would be too energetically unstable to form. So, whenever you see methyl halides, such as methyl chloride (CH3Cl) or primary, forget about them reacting under the SN1 mechanism.

- SN1 mechanism is favored in polar protic solvents, which are solvents that are capable of hydrogen bonding, such as water, ammonia, etc...

- VERY IMPORTANT: STEREOCHEMICAL CONSEQUENCES OF THE SN1 MECHANISM:

Due to the formation of an intermediate carbocation that is sp2 hybridized in nature, the incoming nucleophile can attack the planar cation from two possible sides, from the front or back, with a 50-50 percent chance of attacking either side. By attacking both sides, a pair of ENANTIOMERS forms. Therefore, keep in mind that in SN1 reactions, A RACEMIC MIXTURE FORMS.

SN2 reactions:


- SN2 mechanism is very favorable for methyl, primary, and sometimes secondary halides, but is slowest with secondary.

- This mechanism NEVER occurs with tertiary halides because they are too sterically hindered, such as a tert-butyl group attached to a particular molecule. So, whenever you see a tertiary halide, do not even think of SN2 occurring. Think SN1 instead.

- The reason why tertiary halides do not undergo SN2 is because is it more difficult for the incoming nucleophile to attack the positively charged carbon attached to the halide.

- SN2 reactions are favored in polar aprotic solvents, which contrary to protic ones, are incapable of hydrogen bonding and include such molecules as
cyclohexene.

- This mechanism occurs all in one step. All bonds are formed and broken at the same time...the bond to the leaving group, which is the halide in this case, is broken and the new bond to the incoming nucleophile is made at the same time. NO INTERMEDIATE CARBOCATIONS ARE FORMED.

VERY IMPORTANT STEREOCHEMICAL CONSEQUENCE OF THE SN2 MECHANISM:

- The incoming nucleophile attacks from the backside, 180 degrees from the departing leaving group. This results in the inversion of configuration whenever the molecule contains a chiral center.

Example: Think of a ring, such as chlorocyclohexane, with the chlorine atom facing forward (on a wedge). This would be a secondary halide, the incoming nucleophile would not attack from the top of the ring, where the chlorine atom is attached, because this would result in electronic repulsion...one chlorine atom rich in electrons and the incoming nucleophile which is also rich in electrons. Therefore, the nucleophile would attack from below the ring, which is precisely 180 degrees below the top where the chlorine is. This would minimize electronic repulsion and the new molecule will have the bond to the nucleophile facing backward (on a dashed line now).


That's all I can think of for the moment. Any other questions, feel free to ask.

-
 
Omg... I think my head is going to explode... lol... its been 3 years since I've takin' orgo... =/ I knew it was a bad idea clickin' on somethin' like this early in the morning.... :scared:
 
DoctorRx1986 said:
Hello 1908PharmD...I took organic chemistry 1 spring of last year, so let's see if i can recall as much as possible. Here's a summary of the reactions:

SN1:

- Occurs with secondary and tertiary halides, but the latter halides react the fastest because they form the most stable carbocations. Secondary halides can also undergo SN1 because secondary carbocations are not that
unstable. However, watch out for carbocation REARRANGEMENTS in which a secondary cation is converted into the more stable tertiary cation by a 1,2 methanide or hydride shift.

- SN1 DOES NOT occur with primary or methyl halides because the resulting carbocations would be too energetically unstable to form. So, whenever you see methyl halides, such as methyl chloride (CH3Cl) or primary, forget about them reacting under the SN1 mechanism.

- SN1 mechanism is favored in polar protic solvents, which are solvents that are capable of hydrogen bonding, such as water, ammonia, etc...

- VERY IMPORTANT: STEREOCHEMICAL CONSEQUENCES OF THE SN1 MECHANISM:

Due to the formation of an intermediate carbocation that is sp2 hybridized in nature, the incoming nucleophile can attack the planar cation from two possible sides, from the front or back, with a 50-50 percent chance of attacking either side. By attacking both sides, a pair of ENANTIOMERS forms. Therefore, keep in mind that in SN1 reactions, A RACEMIC MIXTURE FORMS.

SN2 reactions:


- SN2 mechanism is very favorable for methyl, primary, and sometimes secondary halides, but is slowest with secondary.

- This mechanism NEVER occurs with tertiary halides because they are too sterically hindered, such as a tert-butyl group attached to a particular molecule. So, whenever you see a tertiary halide, do not even think of SN2 occurring. Think SN1 instead.

- The reason why tertiary halides do not undergo SN2 is because is it more difficult for the incoming nucleophile to attack the positively charged carbon attached to the halide.

- SN2 reactions are favored in polar aprotic solvents, which contrary to protic ones, are incapable of hydrogen bonding and include such molecules as
cyclohexene.

- This mechanism occurs all in one step. All bonds are formed and broken at the same time...the bond to the leaving group, which is the halide in this case, is broken and the new bond to the incoming nucleophile is made at the same time. NO INTERMEDIATE CARBOCATIONS ARE FORMED.

VERY IMPORTANT STEREOCHEMICAL CONSEQUENCE OF THE SN2 MECHANISM:

- The incoming nucleophile attacks from the backside, 180 degrees from the departing leaving group. This results in the inversion of configuration whenever the molecule contains a chiral center.

Example: Think of a ring, such as chlorocyclohexane, with the chlorine atom facing forward (on a wedge). This would be a secondary halide, the incoming nucleophile would not attack from the top of the ring, where the chlorine atom is attached, because this would result in electronic repulsion...one chlorine atom rich in electrons and the incoming nucleophile which is also rich in electrons. Therefore, the nucleophile would attack from below the ring, which is precisely 180 degrees below the top where the chlorine is. This would minimize electronic repulsion and the new molecule will have the bond to the nucleophile facing backward (on a dashed line now).


That's all I can think of for the moment. Any other questions, feel free to ask.

-
Click to expand...
Wow... I can't wait to take O. Chem this Fall.
 
here's a toughy for you guys:

(this is just to test your skills... the answer will be posted later)


If you have 1-methyl-2-nitrobenzene and you are trying to place another methyl group on the ring...

a) how do you accomplish the addition???

b) what position on the ring will the new methyl group add to???
 
faulkner41 said:
here's a toughy for you guys:

(this is just to test your skills... the answer will be posted later)


If you have 1-methyl-2-nitrobenzene and you are trying to place another methyl group on the ring...

a) how do you accomplish the addition???

b) what position on the ring will the new methyl group add to???
Click to expand...

We havent started talking about that yet. Maybe the Para position ? guessing. idk
 
faulkner41 said:
here's a toughy for you guys:

(this is just to test your skills... the answer will be posted later)


If you have 1-methyl-2-nitrobenzene and you are trying to place another methyl group on the ring...

a) how do you accomplish the addition???

b) what position on the ring will the new methyl group add to???
Click to expand...


Wow it's been a while...I would double check this but....

CH3 is an o,p director, while NO2 is a meta director.

The methyl group will dominate where the new methyl will be placed, since it is an activator (whereas the NO2 is a deactivator)

ortho from the methyl group is positions 2 and 6
para from the methyl group is position 4

Since the nitro is already on position 2, the new methyl will most likely go to the para position to prevent steric hindrance.

Hopefully I didn't confuse you! I almost confused myself...it's been awhile.
 
To complete the addition you need to have CH3Cl/AlCl3. The Cl leaves and the CH3 can attach. I think it's called the Friedel rxn.

Someone confirm this? I should probably review this stuff before pharm school this fall :laugh:
 
good call on the para position...

in competition between ortho/para and meta directors, all things being equal, the OP director wins out... steric hindrance dominates making the major product the para product about 97% of the time...

this is the same kind of process that describes how trinitrotoluene (TNT) is made...

congrats to the smarties out there...
 
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SoccerCoach10 said:
To complete the addition you need to have CH3Cl/AlCl3. The Cl leaves and the CH3 can attach. I think it's called the Friedel rxn.

Someone confirm this? I should probably review this stuff before pharm school this fall :laugh:
Click to expand...


I doubt that'll be necessary. From what i've heard many times, very little organic chemistry is used in pharmacy school except for recollection of basic functional groups and pushing of electrons in classes such as medicinal chemistry. Chances are, you will not be seeing the Friedel-Crafts reaction or the majority of organic reactions such as aldol condensation, the Dieckmann reaction, or the Wittig reaction. Many of these reactions do not occur in the human body. Instead, you'll probably need to have an understanding of nucleophiles, electrophiles, and nucelophilic attacks and not all those reactions. However, i guess all of this also depends on the program. I'll be a student this fall as well, at Nova.
 
SoccerCoach10 said:
To complete the addition you need to have CH3Cl/AlCl3. The Cl leaves and the CH3 can attach. I think it's called the Friedel rxn.

Someone confirm this? I should probably review this stuff before pharm school this fall :laugh:
Click to expand...

I believe that is Friedel Crafts alkylation. I not sure that will work though because the nitro group is a ring deactivator. Friedel alkylation doesn't work when a ring deactivator is on the ring.
 
isn't Sn1 and Sn2 reactions part of O Chem I? I don't see it much often 2nd semester. I learn a bunch of reactions with benzene.
 
Okay, before spring break, we were doing a simple distillation and a fractional distillation experiment. My teacher told us that depending on the pressure we are supposed to subtract 1 or add 1 to the boiling point. I know why that is, which is because you have to make the correction based on the altitude or something like that.

My question is, How do i calculate the pressure based on the temperature for that day. I also know that 1atm = 760mmHG at 25 degrees Celsius. (ithink)

the temp for one day was 57 degrees f (5/9 x 57-32; = 13.9 degrees celsius) and the temp for the other day was 40 degrees farenheit (5/9 x 40-32; = 4.48 degrees celsius). How, then,do i determine the pressure relative to the standard pressure to know if i need to "subtract or add 1"?
 
we did sn1/sn2 e1/e2 in ochem I

It's really not as hard as it seems once you learn the basic rules.

the other problem...
benzene rings are second semester stuff atleast where I took it.

Somebody said something about the friedel rxn not working b/c of the nitro deactivator.. I think that was if the only thing already attached was a deactivator.

I also think it would add para due to steric hindrance with CH3Cl/AlCl3 for the major product.
 
faulkner41 said:
here's a toughy for you guys:

(this is just to test your skills... the answer will be posted later)


If you have 1-methyl-2-nitrobenzene and you are trying to place another methyl group on the ring...

a) how do you accomplish the addition???

b) what position on the ring will the new methyl group add to???
Click to expand...
Tin metal and HCl. The methyl group adds to the 5 position.
 
Congrats! I'm taking it this fall any good tips?

Any help is appreciated!
 
tootoo30 said:
Congrats! I'm taking it this fall any good tips?

Any help is appreciated!
Click to expand...

yeah, Read the entire chapter and work the examples and end of chapter questions before class. Start about 2 days before that chapter. While in class pay attention, and take notes afterwards (sounds funny but I have to listen to his point first and watch his example and answer questions THEN i wrote down the point he just made or the quickest way to get the answer he just arrived at and why). After class read your notes and read that section in your book. (RIGHT AFTER CLASS OR AS SOON AS YOU CAN AFTER CLASS).

lastly the folks on here are pretty helpful if you have any questions after hours .. type it here and someone should help out. :luck:
 
1908PharmD said:
yeah, Read the entire chapter and work the examples and end of chapter questions before class. Start about 2 days before that chapter. While in class pay attention, and take notes afterwards (sounds funny but I have to listen to his point first and watch his example and answer questions THEN i wrote down the point he just made or the quickest way to get the answer he just arrived at and why). After class read your notes and read that section in your book. (RIGHT AFTER CLASS OR AS SOON AS YOU CAN AFTER CLASS).

lastly the folks on here are pretty helpful if you have any questions after hours .. type it here and someone should help out. :luck:
Click to expand...

Yup - in other words, don't procrastinate!!
 
tootoo30 said:
Congrats! I'm taking it this fall any good tips?

Any help is appreciated!
Click to expand...

make sure to work out tons of problems becuase that's the only way to understand the concepts and ask professors and tutors for help whenever you need it, don't wait till last minute. Good Luck! Organic Chem is not as bad as people make it out to be. :)
 
Sparda29 said:
Jeez, I hate Aromatic reactions. My favorites were the condensation reactions and the reactions with the Carboxylic Acid Derivatives.
Click to expand...

Lol...aromatic reactions aren't that bad, can't really do too much with them. Condensation reactions are tough, and reactions with carboxylic acid derivatives are almost all the same....addition/elimination reactions with carbonyls. Well, I like ochem in general...haha. I am tutoring it right now, they already did condensation rxns and all the carbonyl chemistry, just doin aromatic rxns.
 
Thanks everyone for the advice :) I will be taking it with Microbiology and probably a chemistry lab so I should have ample time to study. Again thanks for the advice!
 
Sparda29 said:
The reason why I don't like Aromatic reactions is because you gotta remember that whole chart that tells you what kind of director a group is, and if it is a activator or a deactivator.
Click to expand...


It's not really a chart. I just taught on it yesterday...all you got to remember is that activators are electron donating groups that have LONE PAIRS on them, which contribute to an additional resonance structure on the benzene (added stability). That is why they are called activators. And the activators are ortho, para directing.

For deactivators, they are electron withdrawing groups, and thus the atom attached to the aromatic ring either has a full (+) charge or a partial (+) charge on it. The deactivators do not contribute an extra resonance structure. And the deactivators are meta directing.
 
Here are some tips for o-chem:

- DON'T RELY ON FLASHCARDS. Here's my reasoning why...the first time you write the reaction scheme on a flash card, you are performing the same operation that will be required of you on an exam. After that however, all you are doing is just reading them. You must practice active learning. In o-chem it's so important to write mechanisms and equations down over and over so you can recall it quickly for synthesis problems. The best method to study is to just get reams of computer paper and start writing down reactions grouped into specific categories (regioselectivity, mechanism, etc).

- DON'T rely on tutors or study groups to learn the material, as this can often times be ineffective. Study groups work best when used to clarfiy confusing points or help confirm that you already know the material by providing additional questions/answers.
 
I did well in Organic I, but struggled with Organic II. I love Fisher Projections, but not so much on reactions. The way I made it through was to start re-writing my notes over and over. Looking at them and re-writing them, and repeating this process. Computer paper is best to see the full effect of the reaction diagrams. There are also some people on this website that are VERY good at Organic II, and have reaction diagrams. This is a great resource for anyone needing help in this subject. It is a hard class, but work hard and you will succeed!
 
In pharm. school, organic chemistry on the levels discussed here is worth about as much as an extra elbow.

Taking the class teaches you how to think. While it depends on the school you attend, at our school, basic principles of chemistry (organic or not) is all that's important to know....polarity, acidity/basicity, chiral centers, etc....just the cmpds that have therapeutically important chemistry you will learn about.

Most stuff, it's basic chem. stuff. All the work of synthesis to the drug falls by the way side for the most part....until you go to buy it.
 
justyliz said:
Here are some tips for o-chem:

- DON'T RELY ON FLASHCARDS. Here's my reasoning why...the first time you write the reaction scheme on a flash card, you are performing the same operation that will be required of you on an exam. After that however, all you are doing is just reading them. You must practice active learning. In o-chem it's so important to write mechanisms and equations down over and over so you can recall it quickly for synthesis problems. The best method to study is to just get reams of computer paper and start writing down reactions grouped into specific categories (regioselectivity, mechanism, etc).

- DON'T rely on tutors or study groups to learn the material, as this can often times be ineffective. Study groups work best when used to clarfiy confusing points or help confirm that you already know the material by providing additional questions/answers.
Click to expand...

I tried the first method the first time I took Organic Chem, it did not work. I find the best way is to do every homework problem in the textbook.
 
Sparda29 said:
I tried the first method the first time I took Organic Chem, it did not work. I find the best way is to do every homework problem in the textbook.
Click to expand...

Yeah I think I did every problem in the book maybe 3-4 times total. It worked!
 
acetyl said:
In pharm. school, organic chemistry on the levels discussed here is worth about as much as an extra elbow.

Taking the class teaches you how to think. While it depends on the school you attend, at our school, basic principles of chemistry (organic or not) is all that's important to know....polarity, acidity/basicity, chiral centers, etc....just the cmpds that have therapeutically important chemistry you will learn about.

Most stuff, it's basic chem. stuff. All the work of synthesis to the drug falls by the way side for the most part....until you go to buy it.
Click to expand...


What pharm school do you attend? I know that at some schools, students have to take courses in physical chemistry in addition to the standard biochemistry course. I don't know why some schools implement p-chem into their curriculum, whereas other schools don't consider it useful and don't offer it as such. I'll be attending NSU in the fall and the only pure chemistry course we'll have to take throughout the curriculum is one semester of biochemistry. I thought we would take medicinal chemistry, but apparently, some of its principals are incorporated into a four semester course titled pharmacodynamics. Other schools require plenty of chem.
 
DoctorRx1986 said:
What pharm school do you attend? I know that at some schools, students have to take courses in physical chemistry in addition to the standard biochemistry course. I don't know why some schools implement p-chem into their curriculum, whereas other schools don't consider it useful and don't offer it as such. I'll be attending NSU in the fall and the only pure chemistry course we'll have to take throughout the curriculum is one semester of biochemistry. I thought we would take medicinal chemistry, but apparently, some of its principals are incorporated into a four semester course titled pharmacodynamics. Other schools require plenty of chem.
Click to expand...


Pchem is seriously a death class. Or maybe it's just because my professor sucks. I'm in the third quarter doing statistical mechanics and chemical dynamics, and honestly, it's the hardest stuff ever. We're on kinetics, and the professor assigns problems he never even taught the material on. It's honestly a self-teaching class, but it's hard to self-teach yourself this stuff because the material is so dense.

Pchem for thermodynamics and quantum mechanics/spectroscopy wasn't nearly as bad (but the professors were better...)
 
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