Question

Bis(2,4,5-trifluorophenyl)methanol Scheme 1. Preparation of 5. Br Mg MgBr Oxolane F 5 Scheme 2. Reaction of (2,4,5-trifluorophenyl)magnesium bromide (5) with ethyl formate (3) to form the product of the first step, bis(2,4,5-trifluorophenyl)methanol (4). OH MgBr H F 5 3

Instructions listed below:

I also need help analyzing the TLC. Also the last picture is just a handout that I also I need help on.

I just noticed that the last page is very hard to understand so if you cannot analyze it it's fine.

Answer 1

The given IR spectra are absorbance vs wave-number plots (instead of general transmittance vs wave-number plots). We know that transmittance is inversely proportional to absorbance. Therefore the higher the peaks in the given spectra lesser intense they are. This means, short peaks are the intense bands, high peaks are the weak bands and medium peaks are the medium bands.

Figure 1 : IR spectra of 1-bromo-2,4,5-trifluorobenzene

Peak at 3071 cm^-1 is strong and intense band representing aromatic C-H strech.

Peak at 1327 cm^-1 is strong and intense band representing C-F.

Peak at 625 cm^-1 is strong and intense band representing C-Br.

Peak at 1489 cm^-1 is medium band representing aromatic C=C.

Peak at 731 cm^-1 is strong and intense band representing aromatic C-H bend.

Figure 2 : NMR spectra of 1-bromo-2,4,5-trifluorobenzene

There are only two protons present at position 3 and 6.

Peak at 7.34 ppm is a multiplet of 1H, it represents proton at position 3 which is more deshielded compared to proton at position 6.

Peak at 6.55 ppm is a multiplet of 1H, it represents proton at position 6.

Figure 3 : TLC

Compound 1 is more polar as compared to compound 4. Hence, compount 1 rises more as compared to compound 4 during TLC.

Figure 4 : IR spectra of bis(2,4,5-trifluorophenyl)methanol

Broad band at 3342 cm^-1 represents H-bonded O-H group.

Peak at 2977 cm^-1 is strong band representing alkyl C-H.

Peak at 1333 cm^-1 is strong band representing C-O.

Peak at 1089 cm^-1 is strong band representing C-F.

Peak at 3072 cm^-1 is strong band representing aromatic C-H.

Figure 5 : NMR spectra of bis(2,4,5-trifluorophenyl)methanol

Multiplet of 2H at 7.28-7.11 ppm repesents aromatic more deshielded protons at position 3.

td of 2H at 6.84 ppm repesents aromatic protons at position 6.

Singlet at 6.17 ppm represents proton of alkyl CH attached to OH and two aromatic rings.

Singlet at 2.46 ppm represents proton of OH group.