Some O-Chem questions

[Acekiller]

I appreciate some help on these questions.

After going through a whole bunch of MCAT OChem questions, I'm stuck on these and the internet is not helping me out. Could any Ochem folks give me a hand?



Which of the following reagents would most effectively convert a primary alcohol into the corresponding primary alkyl halide?
A. NaBr
B. CH3I
C. Cl2 / hn
D. PCl3

In deciding whether a substrate will undergo an SN1 or an SN2 reaction, all of the following must be considered EXCEPT the:
A. degree of substitution of the carbon atom bonded to the leaving group.
B. leaving group ability.
C. basicity of the incoming group.
D. solvent.
E. nucleophilicity of the incoming group.


What is the reaction mechanism by which 1-bromo-3,5,6-trimethylheptane reacts with sodium thiomethoxide to form a thioester?
A. SN1
B. SN2
C. E1
D. E2
E. Electrophilic aromatic substitution


Elimination of H-Br from 3-bromo-4-methylheptane can occur to give several different products. The most thermodynamically stable possible product is:
A. 4-methylheptene
B. 4-methylhept-2-ene.
C. 4-methylhept-3-ene.
D. 4-methylhept-4-ene.
E. 4-methyleneheptane.


Elimination reactions can be favored over substitution reactions by all of the following EXCEPT:
A. use of a strong base.
B. heat.
C. use of a poor nucleophile.
D. use of a good leaving group.


Alcohols have higher boiling points than might be expected due to:
A. the Woodward–Hoffman rules.
B. the Cahn–Ingold–Prelog rules.
C. the Thorpe–Ingold effect.
D. the anomeric effect.
E. hydrogen bonding.


Which one of the following types of reaction conditions are ethers NOT stable to?
A. Oxidation
B. Reduction
C. Strong acid
D. Strong base



When an unsaturated hydrocarbon is reduced to an alkane by addition of molecular hydrogen in the presence of a metal catalyst, the reaction is called:
A. hydrolysis.
B. hydroformylation.
C. hydration.
D. hydrogenation.



In a Friedel–Crafts alkylation reaction of toluene, the tolune acts as:
A. a nucleophile.
B. an electrophile.
C. an amphiphile.
D. a leaving group.


17. Addition of ethylene glycol to acetaldehyde will form a:
A. hemiketal.
B. hydrate.
C. cyclic acetal.
D. Schiff base.

Addition of methylamine to propanal followed by heating will produce an:
A. amine.
B. amide.
C. imide.
D. imine.

The product of an aldol condensation is:
A. an a,b-unsaturated carbonyl compound.
B. a 1,3-dicarbonyl compound.
C. a 1,5-dicarbonyl compound.
D. a 1,3-diol compound.


If the ester group of ethylacetoacetate were hydrolyzed to give the corresponding b-ketoacid, subsequent
heating would form a new organic compound and:
A. H2O.
B. CO2.
C. HCl.
D. CO.


Treatment of tristearin (a triester) with base and heat induces ester hydrolysis to form which of the
following?
I. Alcohols
II. Carboxylic acids
III. CO
A. I only
B. II only
C. I and II only
D. I, II, and III


Esters can be synthesized by the addition of the appropriate alkoxide to the appropriate acid halide.
In this reaction, the first two mechanistic steps are:
A. nucleophilic addition / elimination.
B. nucleophilic addition / substitution.
C. electrophilic addition / elimination.
D. electrophilic addition / substitution.


Of the following carboxylic acid derivatives, which one is LEAST reactive toward nucleophilic addition?
A. Ester
B. Amide
C. Acid halide
D. Acid
E. Acid anhydride


In a given ether solution containing a phenol, an amine, and a complex neutral organic molecule, the
phenol can most easily be extracted from the mixture by using:
A. a neutral aqueous extraction solvent.
B. an acidic aqueous extraction solvent.
C. a basic aqueous extraction solvent.
D. sodium sulfate.



In a Diels–Alder reaction between ethyne and 1,3-butadiene, the product is:
A. 1-cyclohexene.
B. 1,2-cyclohexadiene.
C. 1,3-cyclohexadiene.
D. 1,4-cyclohexadiene.

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[Venicat]

I appreciate some help on these questions.

After going through a whole bunch of MCAT OChem questions, I'm stuck on these and the internet is not helping me out. Could any Ochem folks give me a hand?



Which of the following reagents would most effectively convert a primary alcohol into the corresponding primary alkyl halide?
A. NaBr
B. CH3I
C. Cl2 / hn
D. PCl3

In deciding whether a substrate will undergo an SN1 or an SN2 reaction, all of the following must be considered EXCEPT the:
A. degree of substitution of the carbon atom bonded to the leaving group.
B. leaving group ability.
C. basicity of the incoming group.
D. solvent.
E. nucleophilicity of the incoming group.


What is the reaction mechanism by which 1-bromo-3,5,6-trimethylheptane reacts with sodium thiomethoxide to form a thioester?
A. SN1
B. SN2
C. E1
D. E2
E. Electrophilic aromatic substitution


Elimination of H-Br from 3-bromo-4-methylheptane can occur to give several different products. The most thermodynamically stable possible product is:
A. 4-methylheptene
B. 4-methylhept-2-ene.
C. 4-methylhept-3-ene.
D. 4-methylhept-4-ene.
E. 4-methyleneheptane.


Elimination reactions can be favored over substitution reactions by all of the following EXCEPT:
A. use of a strong base.
B. heat.
C. use of a poor nucleophile.
D. use of a good leaving group.


Alcohols have higher boiling points than might be expected due to:
A. the Woodward–Hoffman rules.
B. the Cahn–Ingold–Prelog rules.
C. the Thorpe–Ingold effect.
D. the anomeric effect.
E. hydrogen bonding.


Which one of the following types of reaction conditions are ethers NOT stable to?
A. Oxidation
B. Reduction
C. Strong acid
D. Strong base



When an unsaturated hydrocarbon is reduced to an alkane by addition of molecular hydrogen in the presence of a metal catalyst, the reaction is called:
A. hydrolysis.
B. hydroformylation.
C. hydration.
D. hydrogenation.



In a Friedel–Crafts alkylation reaction of toluene, the tolune acts as:
A. a nucleophile.
B. an electrophile.
C. an amphiphile.
D. a leaving group.


17. Addition of ethylene glycol to acetaldehyde will form a:
A. hemiketal.
B. hydrate.
C. cyclic acetal.
D. Schiff base.

Addition of methylamine to propanal followed by heating will produce an:
A. amine.
B. amide.
C. imide.
D. imine.

The product of an aldol condensation is:
A. an a,b-unsaturated carbonyl compound.
B. a 1,3-dicarbonyl compound.
C. a 1,5-dicarbonyl compound.
D. a 1,3-diol compound.


If the ester group of ethylacetoacetate were hydrolyzed to give the corresponding b-ketoacid, subsequent
heating would form a new organic compound and:
A. H2O.
B. CO2.
C. HCl.
D. CO.


Treatment of tristearin (a triester) with base and heat induces ester hydrolysis to form which of the
following?
I. Alcohols
II. Carboxylic acids
III. CO
A. I only
B. II only
C. I and II only
D. I, II, and III


Esters can be synthesized by the addition of the appropriate alkoxide to the appropriate acid halide.
In this reaction, the first two mechanistic steps are:
A. nucleophilic addition / elimination.
B. nucleophilic addition / substitution.
C. electrophilic addition / elimination.
D. electrophilic addition / substitution.


Of the following carboxylic acid derivatives, which one is LEAST reactive toward nucleophilic addition?
A. Ester
B. Amide
C. Acid halide
D. Acid
E. Acid anhydride


In a given ether solution containing a phenol, an amine, and a complex neutral organic molecule, the
phenol can most easily be extracted from the mixture by using:
A. a neutral aqueous extraction solvent.
B. an acidic aqueous extraction solvent.
C. a basic aqueous extraction solvent.
D. sodium sulfate.



In a Diels–Alder reaction between ethyne and 1,3-butadiene, the product is:
A. 1-cyclohexene.
B. 1,2-cyclohexadiene.
C. 1,3-cyclohexadiene.
D. 1,4-cyclohexadiene.

answers in bold

 

[sv3]

Elimination reactions can be favored over substitution reactions by all of the following EXCEPT:
A. use of a strong base.
B. heat.
C. use of a poor nucleophile.
D. use of a good leaving group.


Does a poor nucleophile mean it is a strong base? Just wondering why the answer is not C? I didn't think the presence of a poor nucleophile meant that elimination would proceed.

thanks
sv3

 

[JJMrK]

Elimination reactions can be favored over substitution reactions by all of the following EXCEPT:
A. use of a strong base.
B. heat.
C. use of a poor nucleophile.
D. use of a good leaving group.


Does a poor nucleophile mean it is a strong base? Just wondering why the answer is not C? I didn't think the presence of a poor nucleophile meant that elimination would proceed.

thanks
sv3

I believe C is not the answer because a poor nucleophile won't be inclined to add to the carbon, whereas a strong nucleophile can come in and attack the carbon, forcing an SN2 reaction.

I don't think it's totally clear, it's just that D is a much better answer than C. The leaving group needs to leave in elimination and substitution reactions and doesn't influence which will occur. It has to be the answer.

 

[chemtopper]

I believe C is not the answer because a poor nucleophile won't be inclined to add to the carbon, whereas a strong nucleophile can come in and attack the carbon, forcing an SN2 reaction.

I don't think it's totally clear, it's just that D is a much better answer than C. The leaving group needs to leave in elimination and substitution reactions and doesn't influence which will occur. It has to be the answer.

Yes ,a poor nucleophile will favor elimination reaction because than it has less tendency to attach with the carbon of the substrate.


A strong base can be poor nucleophile if it is bulky in nature .

 

[sv3]

I believe C is not the answer because a poor nucleophile won't be inclined to add to the carbon, whereas a strong nucleophile can come in and attack the carbon, forcing an SN2 reaction.

I don't think it's totally clear, it's just that D is a much better answer than C. The leaving group needs to leave in elimination and substitution reactions and doesn't influence which will occur. It has to be the answer.

thanks this makes sense now - i forgot to consider that the LG needs to go in both types of reactions (in my head i always think more about the LG in substitutions - so that choice applied to both reactions, leaving only D that fits)

 

[LateBl00meR]

acekiller, you need to reread the first four organic chapter of whichever prep company book you are using. Some of these are extremely basic questions (i.e. H-bonding in alcohols).

 

[pierrot1111]

Hmm...maybe I'm wrong but it seems some of the answers for the O-chem questions seem suspect.



"In a Diels–Alder reaction between ethyne and 1,3-butadiene, the product is:
A. 1-cyclohexene.
B. 1,2-cyclohexadiene.
C. 1,3-cyclohexadiene.
D. 1,4-cyclohexadiene. "

I have no idea what a Diels-Alder reaction is, but I do know what an ethyne and 1,3-butadiene looks like. If a cyclical structure were to be made...I would assume that there will be some pi bonds jumping around and I ended up with something that looks like D. Sorry if my logic/reasoning sounds weird.


"17. Addition of ethylene glycol to acetaldehyde will form a:
A. hemiketal.
B. hydrate.
C. cyclic acetal.
D. Schiff base. "

I don't know what ethylene glycol looks like, but I assume it's some type of alcohol. But I would assume that the alcohol will attack the carbonyl of acetalaldehyde to give something that looks like an acetal, rather than a ketal. So, wouldn't the answer be C?

"Of the following carboxylic acid derivatives, which one is LEAST reactive toward nucleophilic addition?
A. Ester
B. Amide
C. Acid halide
D. Acid
E. Acid anhydride "

It feels like there should be a better answer than D. Since nucleophiles want to lose their electrons somewhere, they probably want to dump them on the most "positive" place/atom there is. Since we are dealing with a carbonyl-thing, then the carbon should be where the nucleophile wants to dump its load. Thus, the less positive the carbon is, the less appealing the nucleophile. The hydroxl group attached to the carbonyl is quite a strong electron donator, but an amine is as well and probably moreso. Thus, I would have to argue that B is probably right.

Feel free to correct me.

 

[Aggro]

Feel free to correct me.

You are correct for all of 'em.

[I'm an idiot. Corrected later.

For question 17, ethylene glycol forms a cyclic acetal when reacted with any ketone or aldehyde. This is the whole idea behind "protecting" ketones during reaction mechanisms. The answer is C.

For question 18, the order of nucleophilic reactivity for carboxlyic acid deriatives goes acid halide > acid anhydride > ester ~=~ carboxylic acid > amide. The answer is B.

 

[BerkReviewTeach]

• Originally Posted by sv3

Elimination reactions can be favored over substitution reactions by all of the following EXCEPT:
A. use of a strong base.
B. heat.
C. use of a poor nucleophile.
D. use of a good leaving group.


Does a poor nucleophile mean it is a strong base? Just wondering why the answer is not C? I didn't think the presence of a poor nucleophile meant that elimination would proceed.

thanks
sv3

I believe C is not the answer because a poor nucleophile won't be inclined to add to the carbon, whereas a strong nucleophile can come in and attack the carbon, forcing an SN2 reaction.

I don't think it's totally clear, it's just that D is a much better answer than C. The leaving group needs to leave in elimination and substitution reactions and doesn't influence which will occur. It has to be the answer.

I'm not sure that D is a "much better answer than C," but there is definitely some ambiguity in this question and D is the leats bad answer.

Sv3, you are correct that choice C is a possible answer to this question. Because it is a poor nucleophile, it is unlikely to undergo substitution, which doesn't necessarily mean it has to undergo elimination. But if the option for a reaction is either subsitution or elimination, then it is more apt to undergo elimination when the nucleophile is poor.

On choice D, a good leaving group leads to the formation of a carbocation, which can undergo either an E1-reaction or an SN1-reaction. This means that choice D could go either way, depending on the temperature.

This means that the answer choices are:

• A. elimination
  B. elimination
  C. probably elimination rather than subsititution.
  D. could be either elimination or subsititution.

Choice D is the best of the choices, but it's not one of those questions where you feel secure in your choice.

To the OP: Where did you get these questions, because the MCAT does not have any five-answer choice questions.

 

[sv3]

You are correct for questions 17 and 18.

For question 16, the Diels-Alder reaction converts an alkyne and a 1,3-diene to a cyclohexene. The answer is A.

For question 17, ethylene glycol forms a cyclic acetal when reacted with any ketone or aldehyde. This is the whole idea behind "protecting" ketones during reaction mechanisms. The answer is C.

For question 18, the order of nucleophilic reactivity for carboxlyic acid deriatives goes acid halide > acid anhydride > ester ~=~ carboxylic acid > amide. The answer is B.

For the protection of aldehydes and keytones, do you have to use a diol or something that has multiple hydroxyl groups? Ek showed this with ethylene glycol as well. I just want to be able to differentiate between hemiacetal formation, and cyclic acetal formation and I am thinking it has to do with the alcohol that is used. Anyone confirm? (PS - does the MCAT even use ketal nomenclature anymore? my TPR book said they don't - everything is acetal)

Also for 18, I think the answer is B due to the fact that amines are bloody terrible leaving groups - not sure I understood some of the explanation from the poster two posts up

cheers

 

[Aggro]

For the protection of aldehydes and keytones, do you have to use a diol or something that has multiple hydroxyl groups? Ek showed this with ethylene glycol as well. I just want to be able to differentiate between hemiacetal formation, and cyclic acetal formation and I am thinking it has to do with the alcohol that is used. Anyone confirm? (PS - does the MCAT even use ketal nomenclature anymore? my TPR book said they don't - everything is acetal)

Also for 18, I think the answer is B due to the fact that amines are bloody terrible leaving groups - not sure I understood some of the explanation from the poster two posts up

cheers

Yea, no one ever uses ketal nomenclature as far as I know. I guess it's worth knowing tha a hemiketal and a hemiacetal are the same thing though.

As for protecting groups, the best ones are ethylene glycol and 1,3-propanediol. Using those creates a cyclic hemiacetal which is a type of ether, which are typically unreactive to just about everything. However, addition of an acid allows for hydrolysis, restoring the ketone.

 

[sv3]

now i can tell if the cyclic acetal is formed or plane old hemiacetal from the addition of an ROH

 

[BerkReviewTeach]

You are correct for questions 17 and 18.

For question 16, the Diels-Alder reaction converts an alkyne and a 1,3-diene to a cyclohexene. The answer is A.

For question 17, ethylene glycol forms a cyclic acetal when reacted with any ketone or aldehyde. This is the whole idea behind "protecting" ketones during reaction mechanisms. The answer is C.

For question 18, the order of nucleophilic reactivity for carboxlyic acid deriatives goes acid halide > acid anhydride > ester ~=~ carboxylic acid > amide. The answer is B.

Actually Aggro, peirrot44 is right on question 16 as well. The reaction is between ethYNE and 1,3-butadiene, not ethENE and 1,3-butadiene, so it's a spinoff of the diene and alkene reaction you are used to seeing. Only one of the pi-bonds of the alkyne reacts in the cyclization transition state, leaving one pi-bond intact. It will remain in place directly across from the new pi-bond in the 6-membered ring. The final product will have two pi-bonds, making it 1,4-cyclohexadiene. You could have also eliminated choice A because of incorrect IUPAC nomenclature. if there is just one pi-bond in the ring, then you don't need to include the "1" in the name. It would just be cyclohexene.

 

[Aggro]

Actually Aggro, peirrot44 is right on question 16 as well. The reaction is between ethYNE and 1,3-butadiene, not ethENE and 1,3-butadiene, so it's a spinoff of the diene and alkene reaction you are used to seeing. Only one of the pi-bonds of the alkyne reacts in the cyclization transition state, leaving one pi-bond intact. It will remain in place directly across from the new pi-bond in the 6-membered ring. The final product will have two pi-bonds, making it 1,4-cyclohexadiene. You could have also eliminated choice A because of incorrect IUPAC nomenclature. if there is just one pi-bond in the ring, then you don't need to include the "1" in the name. It would just be cyclohexene.

Oh, so it is. Color me stupid.

Thanks for the correction.

 

[sv3]

Diels-Alder reactions?
i didn't see it in their topics list
just checking
thanks

 

[Adamska]

number 18...you guys are wrong. It IS D...carboxylate anions are weaker nucleophiles than even amides...

 

[kia ora]

number 18...you guys are wrong. It IS D...carboxylate anions are weaker nucleophiles than even amides...

yep. as my o-chem teacher liked to say (wrt the nucleophilicity of a carboxylate anion): "this thing's dead"

 

[sv3]

Can you explain why the carboxylic acid is worse? Both Ek and TPR say its the amide due to the terrible leaving group which is strongly basic.

I think we might be talking about different things b/c as far as carboxylic acid derivatives go, amides are the least reactive toward nucleophilic attack...pretty sure of it.....

I am thinking the last two replies are not actually about question 18, but rather the leaving groups of the acid derivatives......

 

[kia ora]

well, the O- of the carboxylate ion is an even worse leaving group than is the NH2 of the amide. the carboxylate ion is the most stable of the carboxylic acid derivatives, because its two resonance forms are of equal energy. so, as it's the most stable of the derivatives it therefore is the least reactive with a nucleophile. usually it gets overlooked, though, and the review books generally (I suppose) just rank reactivity as: acid chloride > anhydride >ester >alcohol >amide. but carboxylate ion belongs there on the bottom rung. if you think about it, a thioester would fit in between acid chloride and anhydride, but you never see that in the rankings.

 

[sv3]

Ek ranks carboxylic acids above esters and amides in terms of reactivity. I

wait just a second.....see if you are saying the RCO- is stable, this would make it a good leaving group and this is why COOH is not the least reactive - it has a good leaving group that is stable once it leaves - being stable is an indicator of a good leaving group (ex. Cl- is the most stable which is why its a great leaving group - the weaker the base the more stable and better the leaving group). the amine is unstable and a strong base, making it a poor leaving group - thus it doesn't want to leave making amides very unreactive. Make some sense (dare I ask) or do i have this wrong?

 

[kia ora]

Ek ranks carboxylic acids above esters and amides in terms of reactivity. I

wait just a second.....see if you are saying the RCO- is stable, this would make it a good leaving group and this is why COOH is not the least reactive - it has a good leaving group that is stable once it leaves - being stable is an indicator of a good leaving group (ex. Cl- is the most stable which is why its a great leaving group - the weaker the base the more stable and better the leaving group). the amine is unstable and a strong base, making it a poor leaving group - thus it doesn't want to leave making amides very unreactive. Make some sense (dare I ask) or do i have this wrong?

no, you're right. the NH2 is a poor leaving group, thus the amide is very unreactive. I'm not talking about RCO- in terms of leaving group ability; what I was trying to say (not very clearly, I guess!) is that if you consider a carboxylate ion O- is a terrible leaving group...it would be O2- if it left, and when do you ever see a leaving group with a -2 charge in o-chem? you don't. a carboxylic acid is more reactive than an amide, for sure. I was taught that a carboxylic acid and an ester are essentially equal wrt reactivity, but that's not really true (my profs told us that for our purposes, we should consider them equally reactive)

 

[sv3]

back to the question at hand..#18. B would be correct - the amide.....right?

 

[kia ora]

back to the question at hand..#18. B would be correct - the amide.....right?

what was the question again? lol. yes, of the choices available, B is the best. but if one of the choices was "carboxylate ion" that would be it. oh, another reason that a carboxylate ion is unreactive with a nucleophile is that it will repel/be repelled by a nucleophile, b/c of the carboxylate ion's negative charge. ok, I'll shut up now!

 

[kia ora]

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[kia ora]

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[kia ora]

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[kia ora]

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[kia ora]

sorry guys, the internet got stuck!

 

[Venicat]

Acids and amides show decreased reactivity towards nucleophilic because addition would disrupt the resonance stabilization with the carboxyl pi bond that you get from the lone pair of the O (of OH) or N (of NH2). The rate limiting step is the addition of the nucleophile, not the departure of the leaving group. All the arguments based on whether OH- or NH2- is a worse leaving group are specious. The reason why any difference is observed between acid and amide reactivity is because (1) a major resonance form of the amide puts a positive charge on nitrogen and is slightly less stable and (2) only as a secondary consideration, the acid has more electron density about the carboxyl carbon--counterintuitive since O is more electronegative than N, but remember the entire group is in resonance.

The Diels-Alder question was wrong, yes. There are two pi bonds in the product. And the ethylene glycol question was also wrong. This is a standard reagent used to form a protecting group.

 

[kia ora]

the arguments are not specious. it's perfectly fine to think in terms of either leaving group ability OR in terms of resonance/induction. both methods get you to the same place. it's just a matter of whatever makes more sense to you

 

[Adamska]

That's a terrible question then, because in many cases (at least in orgo) it is assumed that an answer choice of "acid" assumes dissociation has already occurred.

 

[Doodl3s]

Hmm...maybe I'm wrong but it seems some of the answers for the O-chem questions seem suspect.


"Of the following carboxylic acid derivatives, which one is LEAST reactive toward nucleophilic addition?
A. Ester
B. Amide
C. Acid halide
D. Acid
E. Acid anhydride "

It feels like there should be a better answer than D. Since nucleophiles want to lose their electrons somewhere, they probably want to dump them on the most "positive" place/atom there is. Since we are dealing with a carbonyl-thing, then the carbon should be where the nucleophile wants to dump its load. Thus, the less positive the carbon is, the less appealing the nucleophile. The hydroxl group attached to the carbonyl is quite a strong electron donator, but an amine is as well and probably moreso. Thus, I would have to argue that B is probably right.

Feel free to correct me.

THese are all talking about Addition/elimination reactions at the 'Double bonded O'- carbon.... So you're looking at the ability of the leaving group to get kicked off...

anhydrides and and acyl halides you know do this regularly and esters are fairly good since they give off an alkoxide (RO-) which are alrite on their own... So its between kicking off an (R-NH-) or an (OH-) and kicking off an an NH attached to an R group is a HELL of a lot easier than kicking off an OH group.... OH group is NEVER a leaving group...

Im assuming when they say an acid derivitave of a carboxylic acid they're talking about the ACID itself (ie. RCOOH).... So... D is my answer to that

 

[boaz]

Elimination reactions can be favored over substitution reactions by all of the following EXCEPT:
A. use of a strong base.
B. heat.
C. use of a poor nucleophile.
D. use of a good leaving group.

The answer is B. The amount of heat required depends on each specific reaction, whether substitution or elimination. Amount of heat required is proportional to the activation energy. It is wrong to assume that Ea for eliminations is always higher than for substitutions.

C is a good curve ball, but it's wrong because if we pick a strong base, relative rates of elim/subs depends on hindrance.

 

[Red Leader]

THese are all talking about Addition/elimination reactions at the 'Double bonded O'- carbon.... So you're looking at the ability of the leaving group to get kicked off...

anhydrides and and acyl halides you know do this regularly and esters are fairly good since they give off an alkoxide (RO-) which are alrite on their own... So its between kicking off an (R-NH-) or an (OH-) and kicking off an an NH attached to an R group is a HELL of a lot easier than kicking off an OH group.... OH group is NEVER a leaving group...

Im assuming when they say an acid derivitave of a carboxylic acid they're talking about the ACID itself (ie. RCOOH).... So... D is my answer to that

Couldn't the OH on the R-COOH be protonated after nucleophilic attack to form a water, which would then be a good LG?

Example: nucleophilic acyl substitution of carboxylic acids to esters

 

[Doodl3s]

Elimination reactions can be favored over substitution reactions by all of the following EXCEPT:
A. use of a strong base.
B. heat.
C. use of a poor nucleophile.
D. use of a good leaving group.

The answer is B. The amount of heat required depends on each specific reaction, whether substitution or elimination. Amount of heat required is proportional to the activation energy. It is wrong to assume that Ea for eliminations is always higher than for substitutions.

C is a good curve ball, but it's wrong because if we pick a strong base, relative rates of elim/subs depends on hindrance.

NO... TRUST me on this.. Heat DEFINITELY favors elimination over SN... google it, look at your textbooks whatever.
Its D because leaving group only affects bimolecular vs. unimolecular, not elimination or SN...

and as far as the carboxyl question i answered... i started looking around and found it might actually be the amide.., not OH, but i cant say for sure