[discodermolide]

The fragment has a mass of 15 and contains 3 hydrogen atom, you know this from the hydrogen (proton) NMR.
so we have C₆H₅CH₂O-Unknown fragment of mass 15 containing 3 hydrogen atoms.
what is this unknown fragment of mass 15 containing 3 hydrogen atoms?
Put it another way you have calculated 107 mass before, plus 3 gives 110, leaving 12!

[xxdesigulxx]

lithium?

[discodermolide]

Which element has a mass of 12?

[xxdesigulxx]

please ignore the last comment i wrote. i wrote that earlies. Carbon has a mass of 12

[discodermolide]

Right,
so we now have
C₆H₅CH₂-O-CH₃, (methoxymethyl)benzene is your unknown.

[xxdesigulxx]

omg thank you so much. It is same as methoxytoluene right? and am i missing something from the IR Spectrum? meaning did i name the functional groups right beside the alcohol?

[discodermolide]

The IR does not really tell you much apart from the presence of an aromatic C=C. apart from the OH mistake it's ok.

[xxdesigulxx]

thank you so much for your help.

[discodermolide]

My pleasure.

[orgopete]

The IR does not really tell you much apart from the presence of an aromatic C=C. apart from the OH mistake it's ok.

I do not conclude the IR shows an OH group is present. It is valuable to compare actual spectra with different functional groups to help estimate the magnitude of absorptions. The OH band is rather small compared to the relatively weak CH bands. Overtones and water can give weak absorptions. If an alcohol were present, you would find an OH band is much stronger than than even multiple CH absorptions.

[discodermolide]

Orgopete, did you actually read the entire post? Replies 3 & 4 especially, number 3, from the OP said there was an OH present, number 4, I corrected him and said there was no OH.

So I don't really understand your comment.

[orgopete]

Orgopete, did you actually read the entire post? Replies 3 & 4 especially, number 3, from the OP said there was an OH present, number 4, I corrected him and said there was no OH.

So I don't really understand your comment.

Yes, and I looked at the spectrum. The poster also looked at the spectrum and had concluded the weak band around 3300 cm-1 Indicated an OH. Could both be correct? I presumed the poster was inexperienced and thought the weak peak could have been an OH. My comment was directed to that audience to help them distinguish between an alcohol and the instance in which the some environmental OH or even an overtone of a carbonyl compound could leave a small and weak peak in the OH region.

Please check the spectrum yourself and tell us if the poster mistakenly reported the wrong frequency.

[discodermolide]

Thank you for the clarification, it was not clear to whom you were addressing the comment.
The very small peak in the IR which the poster recorded as being between 3400-3500 cm^-1is very likely traces of water, certainly not an alcohol, which is much more intense. Certainly the OH stretch lies within this region.