Irradiation selection

NOE experiments are useful in the identification of diastereomers468. An example is the stereochemical assignment of photoadducts 4 from maleic anhydrides and thiophene where protons were irradiated selectively and responses of the carbons observed (heteronuclear C HJ-NOE experiments)469. 

Bose, A.K., Banik, B.K., Barakat, K.J. and Manhas, M.S., Microwave-induced organic-reaction enhancement (more) chemistry. 5. Simplified rapid hydrogenation under microwave irradiation-selective transformations of beta-lactams, Synlett, 1993, 575-576. 

In addition, oxidative photocyclization has been applied for the formation oftetra-, penta-, and hexa-cyclic azonia-aromatic compounds via photoinduced quaternization (Scheme 9.22). In order to avoid photodecomposition of the photoproduct, the substrates are irradiated selectively by using Pyrex-filtered light through an aqueous nickel sulfate solution filter [33]. 

Upon irradiation with a Xe lamp (100 W), the typical five-line spectrum characteristic of the nitronyl nitroxide radical 114 (g= 2.0066) was progressively transformed into a seven-line spectrum characteristic of an imino nitroxide radical (Scheme 24). It was proposed that during the irradiation, selective deoxygenation of the radical 114 to the radical 115 had occurred <2003S2145>. 

T ributyltin hydride I irradiation Selective hydrogenation of carbon-carbon double bonds... 

The main mechanisms are illustrated with reference to Scheme 8.14. By having hv as different as possible from (and longer than) hi/, it is possible to irradiate selectively only the complexed form. 

---