Hey there! Sign in to join this conversationNew here? Join for free
    Offline

    1
    ReputationRep:
    You're a saint, thank you so much! <3
    Offline

    8
    ReputationRep:
    When drawing optical isomers in the tetrahedral shape, is there a standard place each group should be? Eg. on amino acids is the COOH drawn on the wedge and the NH2 on the dash? etc.
    Offline

    7
    ReputationRep:
    (Original post by annaj97)
    When drawing optical isomers in the tetrahedral shape, is there a standard place each group should be? Eg. on amino acids is the COOH drawn on the wedge and the NH2 on the dash? etc.
    Nope, you can draw it in any orientation
    Offline

    2
    ReputationRep:
    (Original post by annaj97)
    When drawing optical isomers in the tetrahedral shape, is there a standard place each group should be? Eg. on amino acids is the COOH drawn on the wedge and the NH2 on the dash? etc.
    I tend to draw the R group as the wedge as in its in the middle and the NH2 and COOH on either side with the single H vertically upwards, that way it quite clearly and a-amino acid, but i imagine you are not punished either way
    Offline

    2
    ReputationRep:
    (Original post by Magicalgeofray)
    Attachment 549315Attachment 549307 This is what the mark scheme says on Zwitter ions for this question i was confused too so emailed my teacher, and this was her reply but I am still confused:
    [/font][/font][/font][/font]
    Help on this please as I very confused
    Offline

    15
    ReputationRep:
    (Original post by Magicalgeofray)
    Attachment 549315Attachment 549307 This is what the mark scheme says on Zwitter ions for this question i was confused too so emailed my teacher, and this was her reply but I am still confused:
    [/font][/font][/font][/font]
    Zwitterion is DIPOLAR ion not tripolar or quartpolar so only 2 groups should have a charge
    Only when you add and acid or alkali do the other R groups then gain a charge as it is no longer in the dipolar ion (zwitterion) form
    Offline

    2
    ReputationRep:
    (Original post by tcameron)
    Zwitterion is DIPOLAR ion not tripolar or quartpolar so only 2 groups should have a charge
    Only when you add and acid or alkali do the other R groups then gain a charge as it is no longer in the dipolar ion (zwitterion) form
    Perfect thank you Your explanation is the clearest i have heard
    Offline

    2
    ReputationRep:
    Does anyone know why D20 is used in nmr spectroscopy?

    Also, if anyone has links to nmr and combined spectroscopy practice questions ( like at the end of the paper) I can't find any!

    Thanks
    Offline

    3
    ReputationRep:
    QUESTION: Does carboxylic acid get reduce by NaBH4?
    Offline

    15
    ReputationRep:
    (Original post by Magicalgeofray)
    Perfect thank you Your explanation is the clearest i have heard
    sorry for the bluntness, I was getting tired of other people saying the incorrect things
    Offline

    3
    ReputationRep:
    (Original post by sakuraton)
    QUESTION: Does carboxylic acid get reduce by NaBH4?
    No
    Offline

    8
    ReputationRep:
    Why do only O-H and N-H peaks disappear when you add D2O?
    Offline

    2
    ReputationRep:
    (Original post by greenorange)
    Does anyone know why D20 is used in nmr spectroscopy?

    Also, if anyone has links to nmr and combined spectroscopy practice questions ( like at the end of the paper) I can't find any!

    Thanks
    D2O Undergoes Proton exchange with the Hydrogen atoms (protons). D atoms have an even number of nucleons so are undetected in the NMR spectra and results in no O-H or N-H peaks
    Offline

    8
    ReputationRep:
    (Original post by sakuraton)
    QUESTION: Does carboxylic acid get reduce by NaBH4?
    no, only carbonyls (aldehydes and ketones)
    Offline

    2
    ReputationRep:
    (Original post by Magicalgeofray)
    D2O Undergoes Proton exchange with the Hydrogen atoms (protons). D atoms have an even number of nucleons so are undetected in the NMR spectra and results in no O-H or N-H peaks
    Thanks
    Offline

    15
    ReputationRep:
    (Original post by sakuraton)
    QUESTION: Does carboxylic acid get reduce by NaBH4?
    No it doesn't
    Offline

    3
    ReputationRep:
    (Original post by greenorange)
    Does anyone know why D20 is used in nmr spectroscopy?

    Also, if anyone has links to nmr and combined spectroscopy practice questions ( like at the end of the paper) I can't find any!

    Thanks
    Using D2O swaps the protons of -NH, -OH and -COOH so these don't show up on the spectrum, which helps in identification
    Offline

    3
    ReputationRep:
    (Original post by greenorange)
    Does anyone know why D20 is used in nmr spectroscopy?

    Also, if anyone has links to nmr and combined spectroscopy practice questions ( like at the end of the paper) I can't find any!

    Thanks
    It used to identify OH,SH, NH2 etc. They go through proton exchange and disappear from HNMR peak
    Offline

    2
    ReputationRep:
    (Original post by greenorange)
    Does anyone know why D20 is used in nmr spectroscopy?

    Also, if anyone has links to nmr and combined spectroscopy practice questions ( like at the end of the paper) I can't find any!

    Thanks
    D20 is used when there is a alcohol or amine group because when you add D20, the Deuterium (hydrogen atom with even number of nucleons in nucleus) undergoes proton exchange witht he compound. This means the O-H changes to O-D for example. D doesn not produce a peak on NMR (because of equal nucleons so no spin)
    Therefore you compare the spec before and after adding D20 to identify which peak was caused by O-H/N-H because they can occur over a large range of ppm values so it just makes everything easier
    Offline

    15
    ReputationRep:
    (Original post by annaj97)
    Why do only O-H and N-H peaks disappear when you add D2O?
    Their protons are exchangeable/labile as the D atom can replace the H's
 
 
 
Poll
Who is your favourite TV detective?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.