How many types of nonequivalent protons are present in each of the following molecules? How many signals would you expect each of the following molecules to have in its 1H and 13C spectra? The following compounds all show a single line in their1H NMR spectra. List them as they would appear in an NMR spectrum, e.g. by decreasing chemical shift with the lowest shift to the right. These compounds would appear in a spectrum in the order: (List compounds by letter with no commas.)

A.

Molecule #1: It will have three nonequivalent protons because you obtain one from the alkyne CH group, another nonequivalent set from the CH2 group in the middle, and the last one is from the methyl group (CH3) at the end.

Molecule #2: It will have three nonequivalent protons. Becuase the molecule is symetric about the center, the two middle CH3 groups will be equivalent (first set), then the two CH2 groups are equivalent as well (second set), and lastly the end CH3 groups are equivalent due to the symmetry of the molecule (third set).

Molecule #3: Becuase there is no symmetry in the molecule, each proton set (the protons attached to one carbon) will have a different chemical shift. So there will be 5 nonequivalent protons.

B.

Molecule #1: 4 H-NMR signals becuase the molecule does exhibit some symmetry. One set comes from both CH3 groups as they are identical, then the top right aromatic hydrogen is a second set. The third set comes from the bottom and top left aromatic hydrogen (they are equivalent by symmetry), and lastly the fourth set is from the bottom left hydrogen.

There will be 5 C-NMR signals due to symmetry. The methyl carbons (1 set), the top right carbon (2nd set), the top and bottom right carbon (third set), the top left and bttom carbon (4th set), bottom left carbon (5th set).

Molecule #2: Due to symmetry, there will be 3 H-NMR signals from the top middle hydrogen, top right hydrogen, and top right corner hydrogen (by symmetry you can see that all other protons are some equivalent of one of these three). There will be 4 C-NMR chemical signals: the corners (one set), the right and left middle cabons (2nd set), the quad bodned carbons (the ones at the top/bottom right/left corners of the middle benzene ring) (third set)., and the top and bottom middle carbons (4th set).

Molecule #3: By symmetry, and I think you will be able to see this by now, there will be 3 H-NMR signals and 4 C-NMR signals.

C.

The order will be c, e, a, b, d.

Aldehyde protons appear ar 9-10 ppm, alkene protons are around 5-6 ppm, nitrogen alpha protons are roughly 2 ppm, the aliphatic carbon protons are 0.5-1.5ppm, and the silicon compound (tetramethylsilane (TMS)) is the international standard for H NMR and is thus given an absoprtion of 0 ppm.