Orgo naming question

[Lindlar]

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In the very first question of examkrackers orgo I was asked to identify
methyl beta-2,3,4,6-tetra-O-methyl-D-glucoside

The answer is supposed to be the picture I've shown. I don't understand why the first group is called a methyl group, and not an O methyl group or a methoxy group or something else. A methyl group should just be CH3, correct?

 

[h9i9j9]

typo?

(lol...why so serious...you'll be fine...just chill)

 

[TwoPaddles]

Yeah that's just a typo. But even if you don't have any clue about the answers, here's how you can use process of elimination:

You can easily eliminate choice B, because it does not contain enough carbons as glucose.
(You should know from your orgo content review where the anomeric carbon is and where carbon #6 is located.)
You can eliminate choice C, because β-2,3,4,6-tetra-O-methyl-D-glucoside has an O-methyl (methoxy) group at carbon #6. But choice C has a hydroxyl group on that carbon.

So all we are left is with choices A and D. I know there's a typo in the naming of the compound but you can throw out choice D because the naming does not include "hydroxyl" in it.

Choice A shows you that you have five methoxy groups, as the name suggested (if there was no typo 😀)

 

[sillyome]

Hi,

My question is how do you know that there is 4 O-methyl groups, when it says 2, 3, 4, 6, making it seem as if there are only groups. How does the methyl in the beginning make it 5?

 

[MedPR]

In the very first question of examkrackers orgo I was asked to identify
methyl beta-2,3,4,6-tetra-O-methyl-D-glucoside

The answer is supposed to be the picture I've shown. I don't understand why the first group is called a methyl group, and not an O methyl group or a methoxy group or something else. A methyl group should just be CH3, correct?

Is this really an MCAT question? Complex naming isn't even tested on the MCAT..

 

[MedPR]

Hi,

My question is how do you know that there is 4 O-methyl groups, when it says 2, 3, 4, 6, making it seem as if there are only groups. How does the methyl in the beginning make it 5?

methyl beta-2,3,4,6-tetra-O-methyl-D-glucoside

The "tetra-O-methyl" is how you know there are 4 O-methyl groups. Tetra = four, just as tri = 3.

The structure shown in the op should probably be named beta-1,2,3,4,6-penta-O-methyl-D-glucoside

 

[sillyome]

Thank you! I recorded my question wrongly. I know there is 4 groups from the tetra, but how is it actually 5 from just the methyl in the beginning. That is what I don't understand.

 

[MedPR]

Thank you! I recorded my question wrongly. I know there is 4 groups from the tetra, but how is it actually 5 from just the methyl in the beginning. That is what I don't understand.

What?

 

[MT Headed]

You have a methyl and a tetra-methyl. One methyl plus four more methyls. Five total. Why it is correctly named this way is far beyond the scope of the mcat.

This question, the first question of the first quiz of the first chapter, is trying to teach you two things. One, how to solve mcat style multiple choice questions when you have a slender thread of understanding rather than the complete domination of knowledge that you are used to. It's a useful skill to have, test taking with incomplete knowledge and perhaps a good foreshadowing of your future practice of medicine when you won't necessarily know completely what is going on.

Second it is supposed to scare the living daylights out of you, knock your confidence down, and cause you to purchase the book.

Don't worry, the rest of EK orgo mellows out, and the real mcat is more mellow too.

 

[sillyome]

Thank you both MT headed and MedPR, i understand now. It did scare the living day lights out of me.