[Undergradstudent]

Hello,

I have a test tomorrow and I just wanted someone to clear up a few questions for me.

1. Ozonolysis: I know we can use different solvents to do oxidative or reductive work up (to make a carboxylic or aldehyde respectively) but which ones which? The ones I know are Zn/HOAc (reductive?), DMS (reductive?). Also which one requires CH2Cl2. Is the reaction supposed to be cold?

2. Adding bromine to a benzylic position: can we use Br2, hv or do we HAVE to use NBS?

3. Adding OH to an alkene: what is the need of Hg(OAc)2, NaBH4? I know it adds OH in a markovnikov fashion but couldn't we just use dilute/cold H2SO4, H2O? And what other common reactions is Hg(OAc)2 useful for?

4. Mass Spec: Could someone give a brief explanation on how to read a mass spec output?

Sorry if that's a lot of questions but any help is greatly appreciated!! Thank you SO much in advance. Brief explanations for all questions are welcomed and add anything else important if needed!

[discodermolide]

Hello,

I have a test tomorrow and I just wanted someone to clear up a few questions for me.

1. Ozonolysis: I know we can use different solvents to do oxidative or reductive work up (to make a carboxylic or aldehyde respectively) but which ones which? The ones I know are Zn/HOAc (reductive?), DMS (reductive?). Also which one requires CH2Cl2. Is the reaction supposed to be cold?

2. Adding bromine to a benzylic position: can we use Br2, hv or do we HAVE to use NBS?

3. Adding OH to an alkene: what is the need of Hg(OAc)2, NaBH4? I know it adds OH in a markovnikov fashion but couldn't we just use dilute/cold H2SO4, H2O? And what other common reactions is Hg(OAc)2 useful for?

4. Mass Spec: Could someone give a brief explanation on how to read a mass spec output?

Sorry if that's a lot of questions but any help is greatly appreciated!! Thank you SO much in advance. Brief explanations for all questions are welcomed and add anything else important if needed!

Anything that is a reducing agent can be used for this, NaBH₄, P(OMe)₃, DMS is usually used in CH₂Cl₂.
Addition of bromine to the benzylic position requires NBS. Br₂/UV will brominate the aromatic ring.
The NaBH₄ reduces the Hg(OAc)₂ to H, see http://en.wikipedia.org/wiki/Oxymercuration_reaction
Mass spec, there are several types of Mass spec, to which are you referring. Basically MS gives you a series of peaks corresponding to the mass of the fragments produced. Usually the highest mass is the molecular ion (MW of the molecule), sometimes it comes as M+H or M-H depending upon the MS conditions.
Looking at the fragments you can work out what their structure is this assists in determining the structure of the molecule.

[camptzak]

hey man.

O₃ is an oxidizing agent that can attack alkenes and alkynes to form ketone/ aldehyde and a carboxylic acid. ozone gas can be shot directly over the alkeene or alkyne.

NBS is used because Br₂ is a poisonous gas and not very safe, NBS allows the gas to form and quickly break in solution. either way you need to use hv or a peroxide initiator to induce radical rxns. if you dont not radical reactions compete.

in super super simple terms. you smash a molecule with an electron and you see how far it flys. you have a TOF or time of flight. big molecules have small TOF's small ones have large TOFs

[Undergradstudent]

Hello,

I have a test tomorrow and I just wanted someone to clear up a few questions for me.

1. Ozonolysis: I know we can use different solvents to do oxidative or reductive work up (to make a carboxylic or aldehyde respectively) but which ones which? The ones I know are Zn/HOAc (reductive?), DMS (reductive?). Also which one requires CH2Cl2. Is the reaction supposed to be cold?

2. Adding bromine to a benzylic position: can we use Br2, hv or do we HAVE to use NBS?

3. Adding OH to an alkene: what is the need of Hg(OAc)2, NaBH4? I know it adds OH in a markovnikov fashion but couldn't we just use dilute/cold H2SO4, H2O? And what other common reactions is Hg(OAc)2 useful for?

4. Mass Spec: Could someone give a brief explanation on how to read a mass spec output?

Sorry if that's a lot of questions but any help is greatly appreciated!! Thank you SO much in advance. Brief explanations for all questions are welcomed and add anything else important if needed!

Anything that is a reducing agent can be used for this, NaBH₄, P(OMe)₃, DMS is usually used in CH₂Cl₂.
Addition of bromine to the benzylic position requires NBS. Br₂/UV will brominate the aromatic ring.
The NaBH₄ reduces the Hg(OAc)₂ to H, see http://en.wikipedia.org/wiki/Oxymercuration_reaction
Mass spec, there are several types of Mass spec, to which are you referring. Basically MS gives you a series of peaks corresponding to the mass of the fragments produced. Usually the highest mass is the molecular ion (MW of the molecule), sometimes it comes as M+H or M-H depending upon the MS conditions.
Looking at the fragments you can work out what their structure is this assists in determining the structure of the molecule.

1. What about Zn(HOAc)? Is that also considered a reducing agent? Also what are some oxidizing agents?
2. I thought radical bromination would attack benzene last due to benzene's stability.
3. Thanks!
4. Sorry, I don't know which type. Could you expand on the M+H and M-H peaks?

Thank you for the response!

[discodermolide]

Zinc acetic acid is a reducing agent.
Oxidising agents cannot be used to destroy the ozonide, as it is itself an oxidizing agent.

Some oxidising agents are dichromate, hypervalent iodine compounds, oxygen, ozone, conc. nitric acid, perchlorates, perorates, etc.
Br2/UV will brominate the aromatic ring. NBS is used for bromination of the side chains. Some aromatic bromination may occur but it will be very small amounts.

[camptzak]

the benzylic position is very reactive. the benzylic position means the carbon directly attached to the ring. the ring itself is not attacked because, like you said, it is very stable.

[camptzak]

good luck on your test. Im a undergraduate senior at a school called SUNY ESF in NYS. Im majoring in chemistry... of course. Im not as knowledgeable as this other fellow, but I hope i helped!

[Undergradstudent]

Zinc acetic acid is a reducing agent.
Oxidising agents cannot be used to destroy the ozonide, as it is itself an oxidizing agent.

Some oxidising agents are dichromate, hypervalent iodine compounds, oxygen, ozone, conc. nitric acid, perchlorates, perorates, etc.
Br2/UV will brominate the aromatic ring. NBS is used for bromination of the side chains. Some aromatic bromination may occur but it will be very small amounts.

Thank you!
I added some more to my last response!

Sorry, I meant to say oxidative work-up (not agent) but I think I got the answer now though (H2O2).

[Undergradstudent]

good luck on your test. Im a undergraduate senior at a school called SUNY ESF in NYS. Im majoring in chemistry... of course. Im not as knowledgeable as this other fellow, but I hope i helped!

Thank you!
I need all the help and luck I can get. 

[discodermolide]

Zinc acetic acid is a reducing agent.
Oxidising agents cannot be used to destroy the ozonide, as it is itself an oxidizing agent.

Some oxidising agents are dichromate, hypervalent iodine compounds, oxygen, ozone, conc. nitric acid, perchlorates, perorates, etc.
Br2/UV will brominate the aromatic ring. NBS is used for bromination of the side chains. Some aromatic bromination may occur but it will be very small amounts.

Thank you!
I added some more to my last response!

Sorry, I meant to say oxidative work-up (not agent) but I think I got the answer now though (H2O2).

I may be wrong, but I am not aware of an oxidative work-up for ozonoylsis reactions.
The ozonide itself is a strong oxidant.

[Undergradstudent]

Zinc acetic acid is a reducing agent.
Oxidising agents cannot be used to destroy the ozonide, as it is itself an oxidizing agent.

Some oxidising agents are dichromate, hypervalent iodine compounds, oxygen, ozone, conc. nitric acid, perchlorates, perorates, etc.
Br2/UV will brominate the aromatic ring. NBS is used for bromination of the side chains. Some aromatic bromination may occur but it will be very small amounts.

Thank you!
I added some more to my last response!

Sorry, I meant to say oxidative work-up (not agent) but I think I got the answer now though (H2O2).

I may be wrong, but I am not aware of an oxidative work-up for ozonoylsis reactions.
The ozonide itself is a strong oxidant.

Alright, thanks!
Could you expand on the M+H and M-H peaks for Mass Spec?
Or just generally, how would we know if a halide is present?

[discodermolide]

Halides can be detected in the Mass spec. by the presence of their isotopes. Chlorine has two, 35 & 37 in a ratio of 3:1.
So if you see such peaks it infers the presence of chlorine. Bromine is similar it has 79 and 81 with a ratio of 1:1.
M+H, depending upon the Mass Spec. instrument conditions you may observe a M+H peak, this appears when the radical cation picks up a proton from solvent or another molecule. Have a look at http://en.wikipedia.org/wiki/Mass_spectrometry

[Undergradstudent]

Thank you for all your quick responses! 

[orgopete]

Br2/UV will brominate the aromatic ring. NBS is used for bromination of the side chains. Some aromatic bromination may occur but it will be very small amounts.
.
I may be wrong, but I am not aware of an oxidative work-up for ozonoylsis reactions.
The ozonide itself is a strong oxidant.

Although the poster's deadline has past, let me add.

Br2 + Lewis acid (FeBr3) to brominate aromatic ring.
Generating Br• will brominate alkyl chains, preferably at benzylic positions.
By product of NBS is succinimide and Br2 is HBr.

CH3CH=CHCH3 + O3  C4H8O3 (ozonide)
C4H8O3 + H2O  2CH3CHO + H2O2
CH3CHO + H2O2  CH3COOH + H2O

If the alkene is mono- or disubstituted, you need additional H2O2 or equivalent to reach a carboxylic acid oxidation state. Practically speaking, this is not a good reaction sequence to follow if a ketone is one of the products as these conditions are also good for a Baeyer-Villiger oxidation and thus esters can accompany the products. It is better to use reductive workup and then oxidize separately in those cases.