phenol HNMR

[caffeine jitters]

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Hey, guys
I am wondering what the deal is regarding Phenol's HNMR signal. In mikes videos, he says it is 10 ppm, along with aldehydes. Then on BC exam 4, he says it is 5 ppm in the video solution..?

 

[Syxx]

I'm guessing you are talking about the hydroxyl hydrogen shift and not one of the aromatic hydrogens ? One thing about chemical shifts is that they occur within a range that is characteristic for a given group. This is because they are dependent on the solvent used, concentration, temperature etc. For example using the hydroxyl hydrogen in phenol, if the solvent is CDCl3 the signal is in the 5-7 range whereas in DMSO it's around 10. 4-10 is a common range given for where to expect the phenol hydroxyl hydrogen shift.

 

[DAT Destroyer]

Hey, guys
I am wondering what the deal is regarding Phenol's HNMR signal. In mikes videos, he says it is 10 ppm, along with aldehydes. Then on BC exam 4, he says it is 5 ppm in the video solution..?

As I teach my students......Never trust an OH or NH2 or NH signal in NMR !!!! These signals can vary GREATLY over a very large range due to factors that include the extent of hydrogen bonding, temperature, and solvent conditions. . These signals can be more upfield than one anticipates. Your best bet is to get the other signals correct then realize that the signals due to these two particular groups can vary greatly . Their precise position is not particularly important in structure determination.

Hope this helps.

Dr. Romano

 

[caffeine jitters]

I'm guessing you are talking about the hydroxyl hydrogen shift and not one of the aromatic hydrogens ? One thing about chemical shifts is that they occur within a range that is characteristic for a given group. This is because they are dependent on the solvent used, concentration, temperature etc. For example using the hydroxyl hydrogen in phenol, if the solvent is CDCl3 the signal is in the 5-7 range whereas in DMSO it's around 10. 4-10 is a common range given for where to expect the phenol hydroxyl hydrogen shift.

As I teach my students......Never trust an OH or NH2 or NH signal in NMR !!!! These signals can vary GREATLY over a very large range due to factors that include the extent of hydrogen bonding, temperature, and solvent conditions. . These signals can be more upfield than one anticipates. Your best bet is to get the other signals correct then realize that the signals due to these two particular groups can vary greatly . Their precise position is not particularly important in structure determination.

Hope this helps.

Dr. Romano

Ah, okay. This all makes much more sense now. Thanks to the both of you!