Is this a quaternary amine?

[MCATin2018orBust]

Hi all,

 

i am prepping for the med school exam (MCAT) and I came across this molecule in my practice questions.

I got the Q wrong and the explanations called this a Quaternary amine. I recognize that the nitrogen atom is Quaternary, but since only 3 of the 4 groups attached to the N are carbons (the last is sulfur), can I still count this as a Quaternary amine? Is tertiary amine with a Quaternary N more accurate? Thanks much.

 

[keyesrussell]

Hi. I realise this response might be a bit late but I'll try to explain nonetheless. This molecule would be tertiary if it was only attached to three carbon atoms (you don't count the sulphur as you rightly pointed out). To be quaternary the nitrogen needs to be charged, allowing it to form an ionic bond with a negative species. This molecule is therefore quaternary. In terms of being more accurate, a molecule cannot be both tertiary and quaternary so if you were formally describing it you would be better off just saying it was a quaternary amine to avoid confusion. Hope this helped.

P.S. I wouldn't be doing myself justice as a biochemist if I didn't speculate that this molecule looks like a cysteine derivative. If anyone knows what this molecule is could they post it? Greatly appreciated.