Proton NMR of flavin adenine dinucleotide (FAD), a cofactor involved in metabolism is presented below.
Figure 1: Molecular structure of FAD labeled with its twelve different types of protons that show peaks on a HNMR.

Figure 2: HNMR of FAD molecule. The intense single peak at 4.8ppm represents the deuterium oxide solvent.

Figure 3: Two singlet peaks at 2.33ppm and 2.4ppm are expected within the range of 2.30ppm as the two methyls are attached to a flavin group on the FAD molecule (type 1 H atoms from figure 1). These two peaks are slightly apart from one another due to the interaction of the top methyl group with a hydroxyl group as the FAD molecule rotates in space. As a result the hydroxyl groups shields the methyl group just enough to separate the two singlets.

Figure 4: A doublet of a doublet at 3.860-3.920ppm and a doublet at 4.020-4.080ppm are illustrated above. The double of a doublet on the third sp3 hybridized carbon (type 6 H from fg.1) of the carbon chain attached to the flavin group is shielded by three hydroxyl groups and it shows diastereotopicity. The chirality of the carbon atom allows the hydrogen atoms to act differently thus resulting in unequal peaks. On the other hand the doublet corresponds to the hydrogen atoms on the first sp2 hybridized carbon that is attached to the flavin group (type 4 H atoms from fg.1) which is shielded by a halogen. Some small peaks are also present however they are ignored as they correlate to error in the spectrum or the low intensity peaks of the solvent.

Figure 5: A doublet of triplets and multiplet are shown at 4.5ppm and 4.250–4.440ppm respectively as expected. The doublet of triplets equates to the hydrogen atoms on the second and the fourth carbon of the carbon chain attached to a flavin group (type 5 H atoms from fg.1) and they are highly shielded by halogens on the surrounding carbons. The multiplet correlates to the number of hydrogens on the furan group of the FAD molecule.

Figure 6: An expected doublet of the H atoms (type 7/8 H atoms fg.1) of a sp2 hybridized carbon attached to the O’s that are bonded to Phosphorus are presented at roughly 5.820 to 5.840ppm. The peaks are expected at 3-4pmm however in this particular case the H atoms are extremely shielded due to the very electronegative nature of P.

Figure 7: A singlet at 7.620ppm and a singlet at 7.540ppm are the H atoms attached to the carbon aromatic ring of the flavin group (type 2 H atom fg.1). Similar to figure 3, one of the hydrogen is shielded by a halogen compared to the other thus resulting in two separate peaks at 7-8ppm.

Figure 8: A singlet at 8.315ppm and a singlet at 7.850ppm are expected as they are the H atoms attached to the adenine group (type 12 H atoms fg.1) of the FAD molecule. The atoms are extremely shielded as they are attached to heteronuclear aromatic rings. Yet one is shielded greater than the other due to the primary amine group attached to one of the carbons that make up the ring.

[This is a very complicated structure and you don't have to assign all of it - but where is proton 11 and 3? Also you use the term halogen but there are no halogens in this molecule JCB]

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