These guidelines can be consulted whenever you are trying to establish the class of an unknown organic compound.

These will have two peaks. The downfield will be the terminal methyls, and the upfield will be the middle methylenes. The upfield signal will be a mixture of five and six heads, indistinguishable.

Overall chemical shifts will be between 0.7 and 1.7.

Hydrogens in methyl groups are the most highly shielded type of proton and are found at chemical shift values (0.7–1.3 ppm) lower than methylene (1.2–1.4 ppm) or methine hydrogens (1.4–1.7 ppm).

Vinyl hydrogen (C=C-H) appears very downfield, around 4.5-6.5. Alkyl carbons appear between 1.6-2.6. Also dubbed alpha carbons.

Shielding decreases as we approach the double-bond. D is further deshielded because it has a carbon next to it, unlike c.

Hydrogens on the e carbon aren’t equivalent as they can be trans or cis, thence the split.

In terminal alkynes (compounds in which the triple bond is in the 1-position), the acetylenic proton appears near 1.9 ppm. It is shifted upfield because of the shielding provided by the pi electrons.

D is actually a CH2. Book got it wrong in the image below.

Proton d is split into a triplet by the two neighboring protons (3 J), and then the triplet is split again into doublets. The type of pattern is referred to as a triplet of doublets.

The 3 J coupling constant is calculated by subtraction, for example, counting from left to right, peak 6 from peak 4 (648.3 – 641.3 = 7.0 Hz). The 4 J coupling constant can also be calculated from the triplet of doublets, for example, peak 6 from peak 5 (643.9 – 641.3 = 2.6 Hz).

In alkyl halides, the alpha hydrogen (the one attached to the same carbon as the halogen) will be deshielded. Coupling with F will occur, but not other halogens.

The variability of this absorption is dependent on the rates of -OH proton exchange and the amount of hydrogen bonding in the solution.

If exchange of the OH is taking place, the hydrogen on the carbon adjacent to COH will not show any coupling with the -OH hydrogen, but will show coupling to any hydrogens on the adjacent carbon located further along the carbon chain.

One may use the rapid exchange of an alcohol as a method for identifying the IOH absorption. In this method, a drop of D2O is placed in the NMR tube containing the alcohol solution. After shaking the sample and sitting for a few minutes, the IOH hydrogen is replaced by deuterium, causing it to disappear from the spectrum (or to have its intensity reduced).

The methine proton at 1.75 ppm has eight neighbors (2x3 + 2), giving it nine peaks. The C proton is split, meaning that it is interacting with D protons, which in turn means that exchange isn’t happening at its highest rate. This means low hydrogen bonding, and thus the C proton is somewhere in between the chemical shift rate (2.5 from 0.5-5).

Methoxy groups (-OCH3) are especially easy to identify as they appear as a tall singlet in this area. Ethoxy (-O-CH2-CH3) groups are also easy to identify, having both an upfield triplet and a distinct quartet in the region of 3.2–3.8 ppm.

In epoxides, due to ring strain, the deshielding is not as great. The hydrogens on the ring appear in the range 2.5–3.5 ppm.

The largest chemical shifts are found for ring hydrogens when electron-withdrawing groups such as -NO2 are attached to the ring. These groups deshield the attached hydrogens by withdrawing electron density from the ring through resonance interaction.

Conversely, electron-donating groups like methoxy (-OCH3) increase the shielding of these hydrogens, causing them to move upfield.

B is more deshielded than a since it has a chlorine next to it, and also because it’s a CH2, not a CH3.

Location of the -NH absorptions is not a reliable method for the identification of amines. These peaks are extremely variable, appearing over a wide range of 0.5–4.0 ppm, and the range is extended in aromatic amines.

The hydrogen on -NH partakes in exchange, similar to alcohols. This gives it a variable range. Although nitrogen is a spin-active element (I = 1), coupling is usually not observed between either attached or adjacent hydrogen atoms, but it can appear in certain specific cases.

The hydrogens alpha to the amino group (d) are slightly deshielded by the presence of the electronegative nitrogen atom. Notice the weak, broad NH absorptions at 1.8 ppm and that there appears to be a lack of coupling between the hydrogens on the nitrogen and those on the adjacent carbon atom. This hints at rapid exchange.

Hydrogens on the adjacent carbon of a nitrile are slightly deshielded by the anisotropic field of the pi-bonded electrons appearing in the range 2.1–3.0 ppm.

Protons appearing in the 9-10ppm are very indicative of an aldehyde group since no other protons appear in this region.

The pattern for B appears as a septet (7) of doublets (2) resulting from coupling with the adjacent two CH3 groups (n = 6 + 1 = 7) and coupling with the aldehyde proton resulting in a septet of doublets (n = 1 + 1 = 2).

Methyl ketones are quite easy to distinguish since they show a sharp three-proton singlet near 2.1 ppm.

Be aware that all hydrogens on a carbon next to a carbonyl group give absorptions within the range of 2.1–2.4 ppm. Therefore, ketones, aldehydes, esters, amides, and carboxylic acids would all give rise to NMR absorptions in this same area. It is necessary to look for the absence of other absorptions (-CHO, -OH, -NH2, -OCH2R, etc.) to confirm the compound as a ketone.

The quartet for the methylene group B is clearly visible at about 1.45 ppm, but it partly overlaps the multiplet for the single proton c (3+3+2+1) appearing at about 1.5 ppm.

The peak in the 3.5- to 4.8-ppm region is the key to identifying an ester. Either of the two types of hydrogens may be split into multiplets if they are part of a longer chain.

The tall singlet (c) at 2.1 ppm integrating for 3 H is the methyl group attached to the C=O group. If the methyl group had been attached to the singly bonded oxygen atom (H3C-O-), it would have appeared near 3.5 to 4.0 ppm.

In carboxylic acids, the hydrogen of the carboxyl group (ICOOH) has resonance in the range 11.0–12.0 ppm. A peak in this region is a strong indication of a carboxylic acid.

Since the carboxyl hydrogen has no neighbors, it is usually unsplit; however, hydrogen bonding and exchange may cause the peak become broadened (become very wide at the base of the peak) and show very low intensity.

As with alcohols, this hydrogen will exchange with water and D2O. In D2O, proton exchange will convert the group to -COOD, and the -COOH absorption near 12.0 ppm will disappear.

The -COOH absorption integrating for 2 H is shown as an inset on the spectrum. This peak is very broad due to hydrogen bonding and exchange.

Proton C is shifted downfield to 3.1 ppm, resulting from the effect of two neighboring carbonyl groups. The normal range for a proton next to just one carbonyl group would be expected to appear in the range 2.1 to 2.5 ppm.

The INH absorptions of an amide group are highly variable, depending not only on their environment in the molecule, but also on temperature and the solvent used.

Because of resonance between the unshared pairs on nitrogen and the carbonyl group, rotation is restricted in most amides. Without rotational freedom, the two hydrogens attached to the nitrogen in an unsubstituted amide are not equivalent, and two different absorption peaks will be observed, one for each hydrogen.

If the nitrogen atom has a large quadrupole moment, the attached hydrogens will show peak broadening (a widening of the peak at its base) and an overall reduction of its intensity.

Hydrogens on a carbon next to a nitro group are highly deshielded and appear in the range 4.1–4.4 ppm.

C is not as shielded as b as it doesn’t have that many protons around it, thence it’s upfield.