[thegreatguyokay]

Hey everyone. So I've been having problems with this ochem question. I have no idea as to how to even begin answering this question.

Compound A has a parent peak of M+ = 95 m/z in its mass spectrum and shows a medium intensity sharp infrared absorption band at 2280 cm. The HNMR of compound A shows 3 signals in a 4:4:1 ratio. Treatment of compound A with hot aqueous acid generates compound B (M+= 113 m/z) can be transformed back to A by using SoCl2. Finally compound B can be transformed with lithium aluminum hydride (ether) then aqueous acid to compound C (M+ = 99 m/z). What are A, B, and C


 How would I go about explaining this and solving?
 Thanks

[zsinger]

I would start by looking at the IR and H-NMR.  Note that once you "elucidate" a functional group, the reagents shouldn't give you a problem.  The reagents are just there to see if you get the correct products from the previous step.  Mastering NMR is something that takes practice (I'm not even all that great at it).  IR was never taught to us, as it is a dying practice with all our computers and such.
                -Zack

[thegreatguyokay]

kk so I think I have the basic structures down however, the numbers (m/z) don't add up.
I have so far for compound A
       
r - C (triple bond)N

compound b

r -c =0
    |
   NH2

for compound c
    H
    |
R-C-NH2
    |
    H

So I need to figure out what the R group is. For compound A no matter what I choose I go over 95m/z.   

[discodermolide]

So your R group could be this structure

Also there is the possibility of carbon chain isomers such as.

or even having the C=C in a different position.
Take your pick, I don't know if you have to supply all the isomers.

[mst]

I think you missed the 4:4:1 H NMR ratio for compound A.  4:4:1 suggests a highly symmetric molecule, the mass an either unsaturated or cyclic molecule. Considering all this your R is most likely meant to be cyclopropyl although I doubt it's giving only three signals.

[discodermolide]

I really wanted the OP to figure that out!

[thegreatguyokay]

kk so I know there is an alkene but I have it at the beginning instead of in the middle like you. Would that be correct as well? I do get the correct m/z though however im not sure if the compound is correct or not...I am not too sure about the 4.4.1 ratio in this question

[discodermolide]

The 4:4:1 ratio in the NMR tells you that there are 3 different sets of protons in this molecule. One must be next to the CN group, which leaves you to find out what the other two sets are.
The R groups I drew were only a starting point for you to get the structure. There are many other possibilities that don't include C=C !

[thegreatguyokay]

kk so here is my new compound...would this make more sense for a 4:4:1

a isopropyl grp - C=C -C - triple bonded to N

That isopropyl and that alkene gives a 4:4 to the triple bonded CN correct?

[discodermolide]

No, sorry that is not correct, an isopropyl group will not give you a 4:4:1 ratio of signals.

Think cyclic, that is, is there a ring system that can fulfil the conditions given for this compound.

[thegreatguyokay]

A cyclo pentane perhaps. I thought about a benzene but then I went over the correct numbers for m/z. But now I don't really know how this is showing a 4:4:1 ratio?
Unless there is one H on the carbon bonded to the triple bonded CN. The one H with the C has two neighbouring carbons with two H showing a 4:1 ratio



cyclopentane - C-triple bonded to N

This sorta makes sense.....what do you think?

[discodermolide]

That is the compound you want. The protons are in a 4:4:1 ratio.

[thegreatguyokay]

omg sweet! Wow first of all thank you so much for continuously guiding me and not telling me the answer. Which is why I think I understand the whole 4:4:1 ratio thing which was driving me insane. Also thank you for being patient with me. It honestly feels so good cracking this insane problem worth quite a bit!