Organic Chemistry Questions!

[vexx]

Hey, i'm trying to work out how to do these any help please:D

1. Which part of an aldehyde or ketone will react with an electrophile?
a. A hydrogen on the alkyl group
 b. The carbonyl carbon atom
 c. The alkyl group
 d. The oxygen atom

2. Which type of electromagnetic radiation generally involves the greatest energy changes?
 a. radio-TV
 b. UV
 c. visible
 d. IR
 e. microwave

3. What compound is produced when isobutyl bromide (1-bromo-2-methylpropane) is subjected to the following sequence of steps:   
-Mg, Et20
-CO2
-H30+
 a. 3-methylbutanoic acid
 b. 3-methylpropanoic acid
 c. 2-methylbutanoic acid
 d. 2-methylpropanoic acid
 e. 2-methylhexanoic acid

thanksss!

[Mao]

1. The oxygen (electron rich) will react with an electrophile (such as H+)

2. In order of decreasing energy (this is the electromagnetic spectrum): gamma > x ray > UV > visible > IR > microwave > radio

3. No idea, and really cbf digging up my first year lecture notes. Though it looks like the Br is substituted for a -COOH group, so I would say c for now.

[Mao]

3. Yeah, it is 2-methylbutanoic acid. The reaction scheme is:

Formation of a grignard reagent:
isobutyl bromide + Mg --(Et2O)--> (CH3)2CHCH2-MgBr [Grignard reagent]

Nucleophilic addition to CO2 [the R group on the Grignard is nucleophilic, thus it will attack the carbon]
(CH3)2CHCH2-MgBr + CO2 ----> (CH3)2CHCH2COO- + MgBr+

Acid workup
(CH3)2CHCH2COO- + H+ --> (CH3)2CHCH2COOH

[vexx]

Thanks Mao!

Excepttt for 3, the answer wasn't 2-methylbutanoic acid, any idea why?

(i don't think im going to do too well at this subj as i do no work for it and my exam is soon-.-)

[Mao]

Thanks Mao!

Excepttt for 3, the answer wasn't 2-methylbutanoic acid, any idea why?

(i don't think im going to do too well at this subj as i do no work for it and my exam is soon-.-)

Because it is 3-methylbutanoic acid... /facepalm, was not thinking straight when I answered it.

Carboxyl group takes precedence, methyl is on the third carbon. Sorry dude

[vexx]

ahh that's cool, thanks:)

question: is cramming really going to work? i've pretty much done no work for the year and considering cramming alll day for a couple of days before exam.. is it likely i am to fail you can be honest!

[Mao]

I am finding myself asking myself that question too, considering I have done nothing other than tute problems, it's going to be a bitch trying to remember everything.

But yes, cramming, surprisingly, does work. Uni exams aren't as convoluted as VCE exams, they don't try to deliberately trick you, and lecturers tend to not have much imagination. =] I've done it for 10 subjects now, worked each time

[vexx]

Haha that's awesomeee. thanks! Hopefully i'm able to do that, never really crammed like this before it's going to be an intense weekend o_o

[Potter]

I can feel your pain vexx. Just gonna go over the 08/09 exams and make sure everything is good. I'm thinking the 10' exam will be very similar.. Seems to be the trend anyway. Except, the 09's inorganic was so much easier than the 08's.

[vexx]

I can feel your pain vexx. Just gonna go over the 08/09 exams and make sure everything is good. I'm thinking the 10' exam will be very similar.. Seems to be the trend anyway. Except, the 09's inorganic was so much easier than the 08's.

haha i am starting studying tonight (im hopeless), and will hopefully go through these exams on mondayy. it's good to know that they wont try and trick us like vce chem^^; goodluck for the exammmmm!

[Potter]

You'll be alright man, just persevere! All the best towards your studies too. By the way, was that last prac we did out of 40 or 50?

[vexx]

You'll be alright man, just persevere! All the best towards your studies too. By the way, was that last prac we did out of 40 or 50?

i really shouldn't have been so last minute though ehh i guess passing is fine since that still leave me with a 60%+ average!
hmmm pretty sure that it was out of 40 considering last two labs were out of a total of 40.

edit, just checked it's out of 50

[jasoN-]

Can anyone help me in naming these structures (attached)?

For the first one I'm guessing it's N-ethyl-N-methylpropanamine, but not too sure

2nd one, there's an ester group and a ketone group, not sure how to name this one.

any help appreciated, thanks

Edit: I think the 2nd one is propyl-3-oxopentanoate, amirite?

[Mao]

Looks right.

[jasoN-]

Just have a question about cis/trans production from alkenes;

A + H2 --(Pd)--> cis-1,2-dimethylcyclohexane + trans-1,2-dimethylcyclohexane

Identify one alkene (A) in each of the following case that gives the product composition of:
i) 100% cis-1,2-dimethylcyclohexane
ii) 100% trans-1,2-dimethylcyclohexane
iii) 50% of each

Not quite sure how to do this. As the cis isomer is more stable, I don't see how you could get the trans isomer, let alone 100% of it.

For i) I'm guessing 1,2-dimethylcyclohexene, but in textbooks i read that it produces ~80% worth of the cis isomer, so not quite sure
ii) Theoretically, I was thinking something like trans-3,4-dimethylcyclohexene, but practically I doubt this is doable.
iii) Maybe trans-2,3-dimethylcyclohexene? Again, not sure.

Help appreciated, cheers.