CIDNP spectroscopy

The CIDNP spectroscopy is an analytical method for the study of reactions via radical pairs expire.

The method is based on chemical-induced dynamic nuclear polarization ( English Chemically induced dynamic nuclear polarization , CIDNP). This is a physical effect that occurs under certain circumstances in nuclear magnetic resonance spectroscopy (NMR spectroscopy) and in which, in addition to the absorption signals, emission signals are also observed. That is why the name RASER ( radiowave amplification by stimulated emission of radiation ) is occasionally used . The cause of the effect, which was discovered by chance in 1967, lies in the reaction of radical pairs in the magnetic field after they have been created by heat or radiation.

Similar methods are ONP and SNP as well as CIDEP and Endor spectroscopy based on electron spin polarization .

Basics

In nuclear magnetic resonance spectroscopy, transitions of atomic nuclei, which are in different energy levels in the magnetic field with opposite spin (e.g. + ½ or −½), from the lower to the higher energy level are induced by radiation of radio waves. Under certain conditions, nuclei can switch from a higher to a lower energy level and emit energy in the form of radio waves. This is used in CIDNP spectroscopy. In radicals, the electron spin and nuclear spin are coupled, which results in nuclear spin polarization, which is also known as energy polarization. As a result, the higher-energy nuclear spin level is occupied more strongly with the spin −½, which in this case leads to the transition from nuclei to the lower-energy level.

For practical purposes, the probe head of an NMR spectrometer is heated or irradiated with focused light in order to generate radicals in the solution. A classic example is the thermolysis or photolysis of benzoyl peroxide in different solvents ( cyclohexanone or carbon tetrachloride ), whereby different radical pairs can be identified via the emission lines depending on the solvent.

application

In general, the method is mainly used today as Photo-CIDNP spectroscopy to investigate systems in which radicals occur as reactive intermediates.

literature

Karl-Gerhard Seifert: Chemically induced dynamic nuclear spin polarization (CIDNP). In: Chemistry in Our Time . 10, No. 3, 1976, pp. 84-93, doi : 10.1002 / ciuz.19760100304

Web links

Jörg Matysik: Photochemically induced dynamic nuclear polarization. (PDF; 4.0 MB) In: 3rd International Training School on Solid-State NMR, Leiden, June 30, 2010. Accessed March 7, 2012 .

Individual evidence

↑ J. Bargon, H. Fischer, U. Johnsen: nuclear magnetic resonance emission lines during rapid radical reactions. I. Admission procedure and examples. In: Journal of Nature Research A . 22, 1967, pp. 1551–1555 ( PDF , free full text).
↑ J. Bargon, H. Fischer: nuclear magnetic resonance emission lines during rapid radical reactions. II. Chemically Induced Dynamic Nuclear Polarization. In: Journal of Nature Research A . 22, 1967, pp. 1556–1562 ( PDF , free full text).
↑ Harold Roy. Ward, Ronald G. Lawler: Nuclear magnetic resonance emission and enhanced absorption in rapid organometallic reactions . In: J. Am. Chem. Soc. tape 89 , no. 21 , 1967, p. 5518-5519 , doi : 10.1021 / ja00997a078 .

[1] J. Bargon, H. Fischer, U. Johnsen: nuclear magnetic resonance emission lines during rapid radical reactions. I. Admission procedure and examples. In: Journal of Nature Research A . 22, 1967, pp. 1551–1555 ( PDF , free full text).

[2] J. Bargon, H. Fischer: nuclear magnetic resonance emission lines during rapid radical reactions. II. Chemically Induced Dynamic Nuclear Polarization. In: Journal of Nature Research A . 22, 1967, pp. 1556–1562 ( PDF , free full text).

[3] Harold Roy. Ward, Ronald G. Lawler: Nuclear magnetic resonance emission and enhanced absorption in rapid organometallic reactions . In: J. Am. Chem. Soc. tape 89 , no. 21 , 1967, p. 5518-5519 , doi : 10.1021 / ja00997a078 .