ATAR Notes: Forum

VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: hifer on November 02, 2007, 06:57:46 pm

Title: Re Peptide link
Post by: hifer on November 02, 2007, 06:57:46 pm

Hi guys, just wondering, when they ask you to circle the peptide link, do you circle the CONH or just CON? Coz this came up in the 2002 paper Section B Q3c, where the examiner's report only circled CON instead of CONH as they do in the textbook...

Can anyone clarify this with me?

Thanks

Title: Re Peptide link
Post by: ninwa on November 02, 2007, 07:02:42 pm

pretty sure on VCAA exams its the CONH

Title: Re Peptide link
Post by: bilgia on November 02, 2007, 07:06:47 pm

yep its CONH

Title: Re Peptide link
Post by: hifer on November 02, 2007, 07:15:01 pm

hi there, I actually tried to clarify this with my teacher and he said that the actually peptide link is between the carbon-nitrogen bond, so when u draw the full structural formula, u shld only circle the C-N bond and not the O and H?

Does anyone else know this?

Title: Re Peptide link
Post by: ninwa on November 02, 2007, 07:29:46 pm

http://www.vcaa.vic.edu.au/vce/studies/chemistry/assessreports/2004/chemassrepex204.pdf

see the answer for question 8a

Title: Re Peptide link
Post by: Collin Li on November 02, 2007, 07:30:18 pm

Quote from: "hifer"

hi there, I actually tried to clarify this with my teacher and he said that the actually peptide link is between the carbon-nitrogen bond, so when u draw the full structural formula, u shld only circle the C-N bond and not the O and H?

Does anyone else know this?

H is not important.. the C=O part must be circled though (shows that it comes from -COOH group)

Title: Re Peptide link
Post by: hifer on November 02, 2007, 07:39:39 pm

ic, thx!

Title: Re Peptide link
Post by: Ahmad on November 02, 2007, 08:29:37 pm

I circle CONH. Would that be considered wrong?

Title: Re Peptide link
Post by: ninwa on November 02, 2007, 08:35:11 pm

Quote from: "ninwa"

http://www.vcaa.vic.edu.au/vce/studies/chemistry/assessreports/2004/chemassrepex204.pdf

see the answer for question 8a

*sigh* read that :P VCAA says circle CONH

Title: Re Peptide link
Post by: Collin Li on November 03, 2007, 10:36:17 am

I said the H is not important. It means counting it or not is not critical.

Personally, I would though. Even though we are used to ignoring hydrogens on carbon chains, we usually never ignore the hydrogens attached to the nitrogen. The N-H is a "residue" of the -NH2 functional group (which partakes in the peptide bond formation), so it should be circled.

I think I should retract my earlier comment about H not being important though, I've convinced myself that CONH is the only answer.