AISTRIO-DB Spectral Database for Organic Compounds,SDBS

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					AIST:RIO-DB Spectral Database for Organic Compounds,SDBS                                 10/13/09 11:49 AM

  SDBS-13C NMRSDBS No. 2967CDS-03-877                               25.16 MHz
  C18 H15 P                                                         0.48 g : 1.5 ml CDCl 3

               ppm        Int.       Assign.

             137.42           243      P      1                               Page 1 of 2
AIST:RIO-DB Spectral Database for Organic Compounds,SDBS                       10/13/09 11:49 AM

             136.97          243       P      1
             134.04          897       P      2
             133.25          897       P      2
             128.53          471              3
             128.53         1000       P      3
             128.26         1000       P      3

 SDBS No. 2967CDS-03-877

 (c) National Institute of Advanced Industrial Science and Technology (AIST)                     Page 2 of 2
     13,                                                                                                                425

             Proton Magnetic Resonance and Electronic Spectra of
                                            By GORDON   SHAW
                                (Chemistry Department, University of Leeds)
                      J. K. BECCONSALL,               M.
                                           ROSEMARY CANADINE, R. MURRAY
(Imperial Chemical Industries Limited, Petrochemical and Polymer Laboratory, The Heath, Runcorn, Cheshire)
MAVEL~    has found that the 25 Mc./sec. proton            We conclude from these results that each com-
magnetic resonance spectrum of triphenylphos-            ponent of the doublet corresponds to one spin
phine in cyclohexane solution is a single peak,          state of the 31P nucleus, and presumably each
whereas other              using different solvents      contains the resonances of the ortho-, meta-, and
have observed two peaks of unequal height with           para-protons of the benzene rings. The suggested
a separation of about 4 c./sec. a t 60 Mc./sec.          scheme is shown in Figure 2. The fine structure
In some case^^,^ the separation between these
peaks has been assigned, incorrectly, to a chemical
shift.                                                   1                                       iOc ,'see.                   I
   We have examined the proton magnetic reson-
ance of triphenylphosphine in several organic
solvents at 60 Mc./sec. (and a t 32"c, except
where stated otherwise). Relatively concentrated
solutions give a single peak; for example, a 1 . 5 ~ -
solution in deuterochloroform gives an asymmetric
peak a t T = 2.8 p.p.m. with a half-width of about
3 c./sec. In dilute solutions ( < 1 ~ a doublet
(splitting = 3.5 f 0.2 c./sec.) is seen, in which
the relative heights and widths of the two peaks are
concentration-dependent, while the areas under
them remain equal, within the limits of accuracy
of our measurements. Spectra a t four different
concentrations in deuterochloroform are shown in
Figure 1. The ratio of the height of the up-field
                                                                                   2 74
                                                                                (b) 0 . 7 2 ~
                                                                                                (c) 0 3 6 ~
                                                                                                                 2 70
                                                                                                              (d) 0 . 0 9 ~   1
peak to the down-field peak is about 2 : 1 in a                                   FIGURE
0.72~-solution,changing gradually to about 1 :2              60 Mc.Isec. 'H n.m.y. spectrum of triphenylphosphine
in a 0.09M-solution.                                         in CDCI,
   The same phenomenon occurs over a similar
range o concentrations in tetrahydrofuran, ace-
tone, and carbon disulphide. In the two latter           arising from chemical-shift differences, with addi-
solvents each component of the doublet shows             tional multiplicity due to proton-proton coupling,
additional smaller, partly resolved, splittings.         is not resolved in practice and only two composite
   The ratio of peak heights is also temperature-        peaks are observed. The relative chemical shifts
dependent: in a dilute solution in tetrahydrofuran       are expected to be dependent on concentration and
a t 60"c the relative height of the up-field peak is     temperature because of molecular interactions
greater than a t 32"c.                                   (magnetic anisotropy, electric reaction field, and
   The equality of areas in the doublet under all        van der Waals forces may all contribute), and this
conditions suggests that the 3.5 c./sec. splitting       dependence would account for the observed
is due to proton31P coupling, and this interpre-         changes in the peak widths. A t relatively high
tation has been confirmed by heteronuclear spin          concentrations (Figure la) the down-field peak is
decoupling experiments on the 40 Mc./sec. proton         apparently so broad that i t merges with the up-
spectrum.6 In solutions in deuterochloroform             field peak.
covering the concentration range 0.09- 1 . 4 4 ~            The differences in chemical shifts between ring
double irradiation a t 16.2 Mc./sec. decouples the       protons are small, in striking contrast to phos-
31Pnucleus ; the proton resonance then collapses         phines of the type Ph,RP and PhR,P, where R
to a single peak with a half-width less than             is H or alkyl, and arylphosphine oxides. A similar
2 c./sec.                                                effect is seen in the spectrum of triphenylarsine,
426                                                                              CHEMICALCOMMUNICATIONS
                                                           By a similar analysis we find a corresponding
                                                           weak band in the spectra of the phenylphosphines
   Chemical shifts   --                                    (Table). Accepting Cullen and Hochstrasser’s
                                                           assignment of the weak band as a m -+m* transition
                                                           and the intense band as an n+n* or charge-
  co u p Ii ngs                                            transfer transition we propose a similar assignment
                                                           for the phosphines. The low-intensity and sinall
                                                           bathochromic shift of the second band indicates
                                                           that the conjugation is not nearly as strong in
                                                           arylphosphines as had been supposed. The
                                                           spectra indicate, however, that conjugation in
                                                           triphenylphosphine, although small, is larger than
                                                           in the other arylphosphines.

                                                           TABLE. Electvopzic spectra of phosphines and phosphine
                                                                              oxides in. ethanol
                                                            Compound     Amax(mp) Emax       Amax(mp)    Emax
                                                            PhEt,P        252.8    3300       273.2        140
                                                            Ph,EtP        251.3    8090       277.8        950
                                                            Ph,P          261.4  11,000       281.7       1250
                                                             Ph,E tPO                         265-0       1370

                     ‘        2
                         FIGURE                               These n.m.r. and spectral results can be explained
          Sche-matic chemical shifts and couplings         if it is assumed that the key mechanism is the
                                                           interaction of the phosphorus p (m)-orbitals with
                                                           the m-orbital systems of the benzene rings. In
where only a single peak of half-width 2 c./sec. is        triphenylphosphine the molecular geometryfo pre-
observed. The coupling constants between 31P               vents rotation of the benzene rings about the
and all the ring protons are similar, with an average      C-P bond. The rings are therefore held in
value of 3-5 c./sec. By contrast, in the 31P               positions where a small but appreciable overlap
spectra of Ph,PH and PhPH,, Akitt et aZ.6 found            occurs between the v-orbitals of the benzene rings
JP-H  (ortho) = 7.9 and 6.6 c./sec. respectively.          and the phosphorus lone-pair orbitals. It seems
Similarly, in a series of triarylphosphine oxides          possible that this interaction, acting in opposition
with para-substituents, Jp-H (ortho) ranged from           to the inductive effect, causes the chemical shift
10-5 to 11.5 c./sec., and Jp-R (meta) from 2.1 to          differences to be less in triphenylphosphine than
3.4 c./sec..l                                              in mono- or di-phenylphosphines where relatively
   In an attempt to find an explanation for these          free rotation of the rings is possible and p - 7 ~ -
results, we have also recorded the electronic              orbital overlap becomes negligible. It also seems
spectra of several arylphosphines, phosphine               likely that proton-3lP coupling in triphenylphos-
oxides, and arsines. For the tervalent phosphine           phine occurs mainly through a mechanism involv-
and arsine compounds most workers6have reported            ing the m-orbital system of the benzene rings,
only one band in the region 230-270 mp. How-               whereas in the other phosphines (Ph,RP, PhR,P)
ever, Cullen and Hochstrassers performed a                 and phosphine oxides the dominant effect is one
Gaussian analysis on the spectra of the phenyl-            involving o-orbit als.
arsines and found a second band hidden under the
long-wavelength tail of the main absorption.                             (Received, May 25th, 1966; Corn. 353.)

    G. Mavel, Compt. rend., 1959,248, 3699.
    J. K. Ruff, Inorg. Chem., 1963,2, 813.
    G. N. LaMar, Ph.D. Thesis, Princeton University, 1964; University Microfilms, Inc., 65-2139.
    R. G. Taylor, Ph.D. Thesis, Princeton University, 1964; University Microfilms, Inc., 65-2159.
    Spin decoupling experiments were kindly undertaken by E. W. Randall and D. Shaw of Queen Mary College,
    J. W. Akitt, R. H. Cragg, and N. N. Greenwood, Chem. Comm., 1966, 134.
  ’ C . E. Griffin, Tetrahedron, 1964, 20, 2399.
  * See e.g., H. H. Jaff6 and M. Orchin, “Theory and Applications of Ultra-violet Spectroscopy,” Wiley, New York,
1962, p. 497.
    W. R. Cullen and R. M. Hochstrasser, J. Mol. Spectroscofiy, 1960, 5, 118.
  lo J. L. Daly, J. Chem. Soc., 1964, 3799.