Directions: You can use any resource, but one that breathes. The quiz is due by

Question

Directions: You can use any resource, but one that breathes. The quiz is due by February 4th. If it is turned in after this time, you will earn a 0. It can be submitted(electronically or paper form. 1. Is cyclobutadiene aromatic? Fully explain your answer. (4 points) 2. Using the following spectral information, determine the name of unknown organic compound A. For full credit, explain why/how the spectral information led you to your answer. (6 points) 1. Mass spectrometer: Molecular ion of 148 m/z IR: strong absorption between 2800 and 3000 cm^-1 . strong absorption at 3050 cm^-1, and strong absorption between 1400 and 1600 cm^-1: NMR: singlet at 2.5 delta units with integration of 3, singlet at 2.0 delta units with integration 9, 2 sets of doublets between 7.0 and 8.0 delta units with integration of 2 each Name of unknown organic compound A:_

Explanation / Answer

The pi electron energy of cyclobutadiene is higher than that of its open-chain counterpart, 1,3-butadiene, and it is therefore said to be anti-aromatic rather than aromatic. &

it should have
4n+2 pi electrons to be aromatic

it has 4 electrons hence it is anti aromatic

In the NMR, the two sets of doublets between 7 and 8 suggests a para-substituted benzene ring.
The unsplit singlet at 2.5 is appropriate for a methyl on a benzene ring.
The unsplit singlet at 2.0 is appropriate for a t-butyl on a benzene ring.
The compound is para-methyl-t-butylbenzene (also named p-t-butyltoluene), MW 148.

It's much easier to do this if they actually show the spectrum.
The t-butyl peak s/b at 1.3, and the methyl s/b at 2.3. The aromatic peaks are at 7.1 and 7.3.

I don't like these questions where you can do it all on one spectrum, but for the IR a better
description would be more specific. The 3050 is from the aromatic C-H stretch,
2800-3000 is the saturated C-H stretch, and there should usually be a strong aromatic C=C right
at 1600, but in this case it actually comes at 1516. That would be confusing, so they said
it comes between 1400 and 1600.

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