100-Mc. Proton Magnetic Resonance Spectra and Double Resonance of Mo nometh y Ideca lins SIR: The 100-Mc. proton magnetic resonance spectra and double resonance of eight monomethyldecalins (11 ) not only fully confirm the structural assignment but independently provide a complete identification of each structure (Figure 1). These eight stereoisomers resulting from hydrogenation of monomethylnaphthalenes were identified originally by application of three criteria: The four 1-methyldecalins were obtained separately from the four 2-methyldecalins by hydrogenation of the respective 1- and 2-methylnaphthalenes. The isomers in each group of four that differ in conformational energy (skew butane interactions) were distinguished by equilibration leaving only the two pairs of cis isomers unresolved. I n each pair, the one having all bridgehead hydrogens on the same side (cis-syn isomer) was identified by its high kinetic yield (+90%) when ruthenium was used as hydrogenation catalyst.
were performed on the same spectrometer on a modified (IO) Varian 3521 integrator. Ordinary absorption spectra were obtained with either an upper or lower 2-kc. per second (wl) sideband. TRANS-SYN-1METHYLDECALIN
If an audio-oscillator is connected to either the r.f. unit or the sweep coils, additional field modulation at a variable frequency (ut)can make a portion of the ref. power available for spin-spin CIS-SYN-1. METHYLDECALIN
Kumber of skew butane interactions
Isomer trans-anti-1 trans-eyn-1 &-an ti-1 cis-syn-1 trans-syn-2 trans-anti-2 cis-svn-2 &-an ti-2
1 3
4 4 0 2 3
3 EXPERIMENTAL
Apparatus. The spectra were measured in dilute solution (ca. loyo),in CDCla on a high-resolution Varian HR-100 spectrometer. Associate double reionance Pxperiments (1, 3 , 4, 6, 7 , 9 )
Table I.
Compound CH, peak frequency GCH-CH3 CH peak frequency Measured splits of CHI group, C.P.S.
98 Equatorial 196.0 7.0
, . , I , ,
,,I,,,
1.0
Figure 1 .
TA1 Equatorial 86.9
(8)
2.0
1.0
PPM
[a)
1 00-Mc. N.M.R. spectra of methyldecalins
36 Axial 122.9 Not measurable
TS2 Equatorial 86.0
TS1 Axial 85.0
60
87
Axial 146.0
Equatorial 172.0
4.2 4.8
CH3 peak frequency GCH-CHI
7.0 C82 88.9 57
CH peak frequency
145.9
169.5
154.0
Measured splits of CH3 group, C.P.S.
3.0
6.2 6.2 6.2
5.5 5.7 6.3
3.4 5.2
PPM
Measured Peak Frequencies and Spin-Splits in Monomethyl Decalins
TA2 Axial 98.0
6.9
I ,
2.0
CA1 85.5 84
6.1
CS1 84.0 70
6.5 6.7 7.0 CA2 82.7 63 145.7
...
5.2 6.4
Orientation Obtained by sideband technique in C.P.S. from T.M.S. a t 100 Mc. Decoupling frequency by double resonance a t 100 Mc. Calculated from above Memured a t 40 Mc./sec. 60 Mc./sec. 100 Mc./sec. Sideband technique as above Actually the decoupling frequency as above Calcd. Measured a t 40 Illc./sec. 60 Mc./sec. 100 Mc./sec. ~~
VOL. 38, NO. 12, NOVEMBER 1966
1783
decoupling or double resonance. When the instrument is operating on the lower 2-kc. per second sideband, protons whose chemical shifts are at higher a p plied field than those to which they are coupled may be decoupled if W Z - W ~ is adjusted to be approximately equal to the separation of the signals being coupled. The frequency difference between w 2 and w1 is not exactly equal to the chemical shift difference of the two groups of spin-coupled nuclei ( d ) , although in general this discrepancy is small. Therefore, the numbers given in Table I, 6 CH-CHI, should be treated as decoupling frequencies rather than exact chemical shifts between methyl and methine resonances. RESULTS A N D DISCUSSION
The rigid trans-decalins gave spectra in which signals due to axial and equatorial hydrogens were well separated (6, 8). KO separation a p peared in the spectra of the flexible cisdecalins. Nuclear magnetic resonance also differentiated between the axially and
equatorially oriented methyl groups in the trans isomers on the basis of chemical shift data and the spin-spin coupling between the hydrogens of the methyl groups and the ring hydrogen at the mebhyl position. When the methyl group was axial, as in trans-syn-1methyldecalin (TS1) or trans-anti-2methyldecalin (TA2), the signal was split into two sharp bands with a separation of 7.0 C.P.S. This is the spinspin coupling constant. When the methyl was equatorial and the coupling hydrogen was axial, as in trans-anti-lmethyldecalin (TAl) or trans-syn-2methyl-decalin (TS2), the chemical shift difference between the methyl and methine was either too small to record a measurable split of the signal or not large enough to obtain the ultimate coupling constant. The methyl groups of the cis-decalins are free to rock between the axial and equatorial conformations. A separation of 6.2 to 6.4 c.p.s. appears to be the ultimate magnitude.
LITERATURE CITED
(1) Anderson, W. A., Phys. Rev. 102, 151 (19.56). ~.~ (2) Anderson, W. A., Freeman, R., J . Chem. Phys. 37, 85 (1962). (3) Balderschwieler, J. D., J. Chem. Phys. 36, 152 (1961). (4) Bloom, A. L., Shoolery, J. N., Phys. Rev. 97. 1261 11955). (5) Clark;, R. ~L.,j. Am. Chem. SOC. 83, 965 (1961). (6) Freeman, R., Whiffen, I). H., Mol. Phys. 4, 321 (1961). \ - - - - ,
(7) Maher, J. P., Evans, D. F., Proc.
Chem. Soc., 208 (1961). (8) Muller, N., Schult,z, P. J., J. Phys. Chem. 68. 2026 (1964). (9) Royden, V., Phys. Rev. 96,534 (1954). (10) Varian Tech. Info. Bulletin, Vol. 111, No. 3, Ins. 1471 (1963). (11) WeitkamD, A. W., Banas. E. M., Johnson, G.‘ D., 142nd Meeting, ACS; Atlantic City, September 1962. I
~
~
\ - - - - I
E. M. BANAS A. W. WEITKAMP Research and Development American Oil Co. Whiting, Ind. T’arian Associates Palo Alto, Calif.
N. 8.
BHACC.4
Catalytic Determination of Molybdate with the PerborateIodide Reaction SIR: Molybdate is known to catalyze a number of redox reactions. Analytical methods based on this catalytic activity have been devised in the case of the following reactions: H202 I- (8, I I ) , KBr03 p-phenetidine (2), malachite green Ti(II1) (6), H202 rubeanic acid (3). The catalytic polarographic wave of molybdate in the presence of nitrate and perchlorate ions has permitted molybdate to be detected at dilutions of 5 x 10-8M (9). This represents the most sensitive limit although greater sensitivity is claimed for two redox reactions above ( 9 , 3). Bognar has reviewed the literature of catalytic methods of determination (2). Svehla and Erdey have discussed the advantages of the chronometric technique ( 7 ) . The direct measurement of reaction rates with a constant velocity reaction stream allows one to study intrinsically faster reaction rates (4). Absorptiometry is a n ideal physiochemical parameter for monitoring small reactant or product concentration changes. If a double beam, recording spectrophotometer is used to monitor a time interval corresponding to 1 to 370 of reaction completeness, the absorbance recorded is directly proportional to the reaction rate. Initial reaction rates are directly proportional to the catalyst concentration, often to the first power. The initial reaction rate c8n also be made proportional to one of the
+ +
1784
+ +
ANALYTICAL CHEMISTRY
reactants initial concentration if the catalyst concentration is held constant and pseudo-first order conditions are realized. Blaedel and Hicks have applied this latter principle to the analysis of glucose samples (1). They also have described a simple, sensitive, double beam colorimeter suitable for monitoring the upstream and downstream cells of the reaction stream. A micro absorptiometric flow cell, suitable for use in commercial double beam recording spectrophotometers, is described elsewhere in this issue ( 5 ) . RES E RVOIRS TANT
/
9 &)
POLYSTALTIC PUMP
UPSTREAM DELAY
EUFFER
SAMPLE
MlXlNC HEAD
LINE UPSTEAM CELL
INTERCELL DELAY
LINE DOWNSTREAM
CELL
WASTE
Figure 1.
Reaction stream schematic
A simple constant velocity stream can be built around a pair of these flow cells. The adaptation of a Cary Model 14 spectrophotometer to accomodate this system is described in this paper. Stock solutions of hydrogen peroxide are unsuitable for use in closed flowing systems because of their decomposition and subsequent outgassing. Perborate is a more stable oxidant. I t s oxidation of iodide is also catalyzed by molybdate. This paper also reports on the use of this reaction in the catalytic analysis of micromolar concentrations of molybdate. EXPERIMENTAL
Apparatus. Figure 1 is a schematic flow sheet of the reaction stream. T h e DumD was a Buchler Polystaltic pump (Buchler Instrument6 Inc., 1367 16th St.. Ft. Lee. N. J. 07025). Three, 100-ml. thermostated borosilicate bottles with 24/40 tops served as reservoirs. Solutions were withdrawn with 1-mm. i.d. capillary tubing. h 2-mm. i d . , 3-way stopcock on top of t h e buffer reservoir, permitted one to alternately inject this blank solution or an unthermostated sample into the stream. The mixing head was made from clear Plexiglas with 1-mm. i.d. capillary inlet and outlet tubing according to previously described techniques (4). The three inlet capillaries were Pymmetrically placed a t right angles to the outlet. Pump lines from the reservoirs to the
