International Joumal of Maw Specrramefry and Ion Processes 123 (1993) 171-185 Elsevier Science Publishers B.V., Amsterdam 171 Experimental and computational studies of deuterated ethanols: gas-phase acidities, electron affinities and bond dissociation energies* Thuy Thanh Dang, Edwin L. Motell’, Michael J. Travers, Eileen P. Clifford, G. Barney Ellison, Charles H. DePuy and Veronica M. Bierbaum Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215 (USA) (First received 2 April 1992; in final form 25 June 1992) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQP Abstract The tandem flowing afterglow-selected ion flow tube has been employed to measure the gas-phase acidities of a family of deuteratcd ethanols. We find that both a and fi deuterated ethanols are weaker acids than undeuterated ethanol with CL dcuteration having a more pronounced &ct. The acidities, relative to undeuterated ethanol [ANti19BI(CH3CH20H) = 377.5 + 2kcalmol-‘1 are AAJf&(CD,CH,OH) = 0.20 * O.l5kcalmol-‘, AA&(CH,CD,OH) = 0.35 & 0.15 kcalmol-’ , andAA&,(CD,CD,OH) = 0.50 f0.15 kcalmol-‘. In aseparate set ofmeasurements, we have studied the negative ion photoelectron spectroscopy of a set ofethoxide ions to determine the electron affinities of the correspond- ing ethoxy radicals. The electron al&ties decrease witbincreasing deuterimn substitution. We find: EA(CH,CH,O) = 39.55 + O.l6kcalmol-‘, EA(CH,CD,O) = 39.48 f O.l6kcalmol-‘, EA(CD,CH,O) = 39.41 * O.l6kcalmol-‘, and EA(CD,CD,O) = 39.27 k 0.16 kcalmol-‘; the relative error bars are f0.05 kcalmol-’ The corresponding O-H bond strengths of the deuterated ethanols can be extracted from these acidities and electron affinities. We find that 01 deuteration increases the O-H bond strength by 0.3 f 0.2 kcal mol-’ while fl deuteration has a negligible effect. The bond dissociation energies, relative to undeuterated ethanol [D,,,(CH,CH,(FH) = 102.2kcalmol-‘1 arc Doon(CD3CH20-H) = 102.3 f 0.2kcaImol~‘, D,,,,(CH,CD,&H) = 102.5 + O.Zkcalmol-I, and &,s(CD,CDzO-H) = 102.5 f 0.2kcalmol-I. Indicated error bars arc relative errors; absolute errors are f 2 kcal mol-‘. Hartree-Fock-SCF calculations were per- formed on the various deuterated and undeuterated ethanols, ethoxy radicals, and ethoxide anions to calculate the relative acidities, electron affinities and bond dissociation energies. The results are in good agreement with our experimen- tal values. Keywords: ab initio calculations; deuterated ethanols; gas-phase acidity; electron affinity; bond dissociation energy; deuterium isotope effects. Introdoction Correspondence 10: V.M. Bierbaum, Department of Chemis- try and Biochemistry, University of Colorado, Boulder, CO 803090215, USA. l Dedicated to Professor Wade L. Fite, an extraordinary scient- ist, teacher and entrepreneur. Professor Fite’s pioneering work contributed substantially to the development of photoelectron spectroscopy as employed in this research; the use of Extr&l quadrupole technology in flowing afterglow and SIFT instru- ments greatly expanded the versatility of these techniques. ’ Permanent address: Department of Chemistry, San Francisco State University, San Francisco, CA 94132, USA. Isotopically labeled ionic and neutral reagents have been widely used in the study of gas-phase reaction mechanisms. In particular, deuterium- labeled reagents and hydrogen-deuterium exchange processes have provided a wealth of information on the structure and isomerization of ions as well as on the details of their reactive pathways. It is therefore surprising that there is relatively little experimental 0168-I 176/93/$06.00 0 1993 Elsevier Science Publishers B.V. All rights reserved