Friday, April 07, 2017

Domelsmith 2, photoelectron spectra of LSD, DMT, indole, and several tryptamines

The photoelectron spectra of DMT and LSD is pictured below. The lowest pi ionization potential of LSD (7.25 eV) is slightly lower than that of N,N-DMT (7.57 eV).

The photoelectron spectrum of LSD revealed 7 ionization potentials between 7.25 and 9.75 eV. Four ionization potentials are assigned to the pi ring system; they are 7.25, 8.05, 8.5, and 9.75 eV. The other 3 ionization potentials of LSD are assigned to the diethylamide group. The amine lone pair ionization energy is 8.4 eV. The carbonyl-nitrogen gives rise to the peak in the 8.8 eV region of the spectra, while the carbonyl pi orbital gives rise to an ionization potential at 9.08 eV.

In the photoelectron spectrum of DMT, 3 ionization potentials are assigned to the pi ring system, and 1 ionization potential energy to the nitrogen lone pair on the side-chain. The pi ionization potentials of DMT occur at 7.6, 8.2, and 9.5 eV, and the tertiary amine lone pair gives rise to an an ionization near 8 eV.

Figure 7 below shows the photoelectron spectra of indole, tryptamine, N-methyl-tryptamine, N,N-dimethyl-tryptamine, 5-methyl-tryptamine, and 5-methoxy-tryptamine.

Tryptamines have a side chain bearing a nitrogen with lone pair orbitals. The ionization potential energy of the nitrogen lone pair falls consistently near 9.0 eV. In the tryptamine spectra, the broad band centered at 9.25 eV is attributed to ionization from the nitrogen lone pair. This ionization potential is lowered from 9.25 eV in tryptamine, to 8.9 eV in N-methyl-tryptamine, and finally to around 8 eV in N,N-dimethyl-tryptamine. Thus we see that the degree of carbon bulk on the side-chain nitrogen, not just the aromatic moiety, can significantly affect the electron-donating ability of the nitrogen lone pair.

In Table I, the first (IP1) and second (IP2) ionization potential energies of several tryptamines are summarized. LSD is the best electron donor in this series, followed by DMT.


Domelsmith L. N., L. L. Munchausen and K. N. Houk (1977). Photoelectron spectra of psychotropic drugs. 1. Phenethylamines, tryptamines, and LSD. Journal of the American Chemical Society 99, 4311-4321. doi:10.1021/ja00455a018