benzene

benzene - [ CONTRIRlTI.ION FROM THE DEPARTMEYT O F...

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[ CONTRIRlTI.ION FROM THE DEPARTMEYT OF CHEMISTRY, MOUNT HOLYOKE COLLEGE] Vacuum Ultraviolet Absorption Spectra of Cyclic Compounds. I. Cyclohexane, Cyclohexene, Cyclopentane, Cyclopentene and Benzene BY LVCY W. PICKETT, MARGARRT MUNTZ AND E. M. ~~CPHERSON The far ultraviolet absorption spectra of the five- and six-membered ring hydrocarbons, cyclohexane, cyclohexene, cyclo- pentane, cyclopentene and benzene have been measured between 45,000 and 64,000 cm.-'. Measurements of intensity have been made by a photographic method using the compounds as flowing vapors to minimize photodecomposition. Val- ues of oscillator strength have been calculated. Applications of the results to the problem of the molecular structure of five- and sixmembered ring compound.; are noted Introduction The molecular structure of five- and six-mem- bered ring compounds has been a subject of much discussion and conflicting evidence. Recent articles by Pitzer2 and co-workers have summarized the extensive studies of infrared and Raman spectra and of thermodynamic properties that have been made by many investigators and have concluded that no one of the four compounds, cyclohexane, cyclopentane, cyclohexene and cyclopentene is planar. Recent infrared and Raman measure- ments by hfiller and Inskeep3 have shown con- clusively that cyclopentane does not have & symmetry. The present paper concerns the spectra of these four compounds as well as that of benzene which is generally treated as a planar hexagon of Dah symmetry. The ultraviolet absorption spectra of these five compounds have been studied but in no case have intensity measurements of the vapor spectrum been reported. The present measurements have been made in tbe Schumann region between about 2200 and 1500 A. Scheibe and Grieneisen4 studied the spectrum of cyclohexane and Klevens and Platt5 noted that the transmission limits of a 0.13 mm. layer of liquid Syclohexane and cyclopentane were 1765 and 1725 , respectively. Carr and Stucklen6a,b have measured the posi- tion of the bands of cyclohexene, cyclopentene and benzene in ,this region. Price and TutteGh have shown photographs of cyclohexene and benzene and have found ionization potentials. Platt, Klevens and Price7 have reported intensity measurements of cyclohexene in heptane solution. The ultraviolet spectrum of benzene has been a subject of much investigation both experimental and theoretical. A careful vibrational analysis of the band system near 2600 has given evidence that the latter is a forbidden transition of type A1g-B2u allowed by an E, vibration. (1) This work has been supported by the ONR under Contract K8onr 74100, NR-055-160 (2) C W Beckett, K S Pitzer and R Spitzer Txrs JOURNAL 69, 2488 (19471, J E Kilpatrick, K S Pitzer and R Spitzer, 161d 2483 (1947), C W Beckett, U K Freeman and K S Pitier ~hzd 70, 4227 (1948) (3) F A Miller and R G Inskeep, J Ckem Pkys , i8, 1519 (1950) (4) G Scheibe and H Gneneisen, Z pkysrk Ckem , BPS, 52 (1934) (5) H B Klevens and J R Platt, THIS JOURNAL, 30.55 (1947) (6) (a) E P Carr and H Stiicklen, J Chem Phys , 6, ii (1918) ih) W C Price and nT T Tutte, Pioc Roy Soc (lomioil) A174, 207 (1 040) (7) J R Platt H R Kleven5 and \V
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This note was uploaded on 04/09/2011 for the course CHEM 99 taught by Professor Staff during the Fall '08 term at UCSB.

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benzene - [ CONTRIRlTI.ION FROM THE DEPARTMEYT O F...

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