Chemistry Exam Revision Questions

[crayolé]

2. Is the OH in carboxy group considered a hydroxy group i.e. can OH (hydroxy) be ionised in basic solution to form O-?

No, it does not ionise (at VCE level). In reality, it can ionise, but you require a VERY strong base (pH > 14 if I remember correctly)

Sorry, maybe I'm reading the question wrong but doesnt the COOH of a COO^- in any basic environment? i.e zwitterions in amino acids and amino acids in basic solution

Also whilst on this topic, at what pH do zwitterions occur?
The overall molecule is positive in acidic environments and negative in basic environments but when is it both?

[kenhung123]

I think in general or at VCE level as Mao refers, it is 7 however in Neap 2010 they specified the isoelectric point of a few amino acids to be pH 6 (which is like their neutral point or something) but I can't believe they would expect us to know all the isoelectric points for each amino acid..

Also I would like to ask, since amino acids turn positive in acidic environments, does it mean they are basic after this reaction? (They are conjugate acid base compounds)

[crayolé]

I think in general or at VCE level as Mao refers, it is 7 however in Neap 2010 they specified the isoelectric point of a few amino acids to be pH 6 (which is like their neutral point or something) but I can't believe they would expect us to know all the isoelectric points for each amino acid..

Also I would like to ask, since amino acids turn positive in acidic environments, does it mean they are basic after this reaction? (They are conjugate acid base compounds)

Yep, they act as a base in acidic environments and vice versa

[kenhung123]

Isn't this 2-chloro-3-methylhex-4-ene?

[m@tty]

No. The double bond takes precedence. So it is 5-chloro-4-methylhex-2-ene.

[kenhung123]

But the IUPAC nomenclature classifies Haloalkanes as primary functional groups and is takes precendence over double and triple bonds..

# Identify the parent hydrocarbon chain (The longest continuous  chain of carbon atoms)
# Identify the functional group, if any (If more than one, use the one with highest precedence as shown here)
http://en.wikipedia.org/wiki/IUPAC_nomenclature_of_organic_chemistry

[m@tty]

Ok, I always thought that the double/triple bond was more important =/

[andy456]

Every exam I have done has marked it correct with the double/triple bond as priority.. (hope that sentence makes sense)
I'm pretty sure this is how you would do it.

[Mao]

2. Is the OH in carboxy group considered a hydroxy group i.e. can OH (hydroxy) be ionised in basic solution to form O-?

No, it does not ionise (at VCE level). In reality, it can ionise, but you require a VERY strong base (pH > 14 if I remember correctly)

Sorry, maybe I'm reading the question wrong but doesnt the COOH of a COO^- in any basic environment? i.e zwitterions in amino acids and amino acids in basic solution

Also whilst on this topic, at what pH do zwitterions occur?
The overall molecule is positive in acidic environments and negative in basic environments but when is it both?

OH, that was a misinterpretation on my part. You are correct in what you say.

An alkanol OH (hydroxy) cannot go to O-.

A carboxyl OH goes to O-. This is rarely referred to as a hydroxyl group.

[Mao]

But the IUPAC nomenclature classifies Haloalkanes as primary functional groups and is takes precendence over double and triple bonds..

# Identify the parent hydrocarbon chain (The longest continuous  chain of carbon atoms)
# Identify the functional group, if any (If more than one, use the one with highest precedence as shown here)
http://en.wikipedia.org/wiki/IUPAC_nomenclature_of_organic_chemistry

Are you sure? I am fairly sure the correct precedence is multiple bond > halides:
http://vcenotes.com/forum/index.php/topic,25368.msg258296.html#msg258296

For that molecule, however, both names will be accepted at VCE level.

[kenhung123]

Oh sorry, I didn't know haloalkane is secondary :S luckily picked this up before exam