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OCR A2 CHEMISTRY F324 and F325- 14th and 22nd June 2016- OFFICIAL THREAD

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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

Reply 1301

sakuraton

QUESTION: Does carboxylic acid get reduce by NaBH4?

Reply 1302

tcameron

Original post by Magicalgeofray

Perfect thank you :smile:

Your explanation is the clearest i have heard

sorry for the bluntness, I was getting tired of other people saying the incorrect things

Reply 1303

Sarcastic Goats

Original post by sakuraton

QUESTION: Does carboxylic acid get reduce by NaBH4?

Reply 1304

annaj97

Why do only O-H and N-H peaks disappear when you add D2O?

Reply 1305

Magicalgeofray

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

Reply 1306

annaj97

Original post by sakuraton

QUESTION: Does carboxylic acid get reduce by NaBH4?

no, only carbonyls (aldehydes and ketones)

Reply 1307

username2221225

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

Reply 1308

tcameron

Original post by sakuraton

QUESTION: Does carboxylic acid get reduce by NaBH4?

No it doesn't

Reply 1309

Sarcastic Goats

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

Reply 1310

sakuraton

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

Reply 1311

CalistaJupiter

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 :smile:

Reply 1312

tcameron

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

Reply 1313

Sarcastic Goats

Original post by annaj97

Why do only O-H and N-H peaks disappear when you add D2O?

Don't forget -COOH

Reply 1314

itsConnor_

Original post by ranz

what about in standard isolectric point

Posted from TSR Mobile

At isoelectric point it exists as zwitterion with NO OVERALL CHARGE (in definition) hence its only COO- and NH3+ and the R group is NOT affected :smile:

Reply 1315

annaj97

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

Why does this only happen with O-H and N-H peaks?

Reply 1316

itsConnor_

Original post by CalistaJupiter

They don't all protonate… I did a past paper that had a 'zwitterion' with an extra cooh side group and the mark scheme said "reject if both cooh groups are shown to have donated a proton" because only groups directly involved in being an amino acid (eg RCH(NH2)COOH) actually protonate