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TRANSCRIPT
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and Paul also demonstrated that a useful correlation can bemade between the chemical shift of a particular carbon atomand the number of carbon atom neighbors located one, two,
' three, four, and five bonds away. The small number ofhighly branched systems in theGrant and Paul set ofparaffinsmade the statistical analysis uncertain for severalof theparam-
describing tertiary and quaternarycarbon atoms.chemical shifts for all paraffin isomers through Q
and many of the readily available
C,
paraffin isomers aregiven here. The large set of paraffin spectra was a greathelp in the development of generally applicable carbon-13chemical shift parameters. A parameter set similar inprinciple to that of Grant and Paul, but different in detail,was developed by testing several possible parameter sets.The best set, described here, fits all the data with a standarderror of estimation of 0.79 ppm. The development of acorrelation for group-type analysis by carbon-13 NMRalso depended heavily upon the large set ofparaffin spectra.
EXPERIMENTALThe spectrometer used in the studies was a standard Varian
HA-100 operating at a frequency of 25 MHz and using 8-mmNMR tubes. The hydrocarbon samples, obtained from theAmerican Petroleum fnstitute and the Chemical SamplesCompany, were diluted 1:1 with dioxane, which served as
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laboratories^may be due to the diiTerenc^nTjolverOs^iiinb^dforjhe measurementsX?)^
(3) R. L. Lichterand J. D. RoherK J Phvi Chem . 74J_9jjJ,l97o)
both the internal reference and as the field-frequency lock Isignal. The chemical shift values for the sample were then Icomputed with respect to tctramethylsilane, using the known [chemical shift of dioxane_with respect to tctramethyl silane C I-tfJXXwL" ■ * \For most of the spectra, the Varian "white noise" de- .coupler was used to eliminate C-H coupling. The chemical ishift assignments were made by comparing the spectra from Lrelated compounds and correlating the systematic shifts due to [ Islight differences in structure, as described by Grant and t-Paul. The assignments show a strong internal consistency £
'
and were checked where necessary by off-resonance decou- Fpling, which permits the C-H magnetic interaction to occur (while still generating some Overhauser enhancement. «'
RESULTSThe experimental chemical shift values for 59 paraffins,
C 5through C,, relative to tetramethyl silane are given inTable I. Our chemical shift values differ slightly fromthose of Grant and Paul. On our spectrometer, the chem-ical shift values were reproducible to within ±0.1 ppm.
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The differences between the chemical shift values
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:~~f^i xAjfc "_»V \ TableL '3 C Chemical Shifts for C 5(o C 9Paraffins
foVfc ] "S =°> CSj = +192.8n\l< ¥ Chemical shift
<-~ -Identification^
C, C, C,
c7~
C, \
A.! XXXCX;- 13.5 22.2 34.1{ C Y"^X 0 .
" 4"" 21 - 9 29 -9 31 6 11.5c
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C|-C,-C,-C« - . . 28.7 30.3 . 36.5 8.5I
C ■X'i'lc C '71 ~/~~
I 1 b
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13.9 18.8 .' , '..- .
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26.8 ' - 11.6 14.5 X "* ■ : - , ;'i
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Continued *
Chemical shift ■ 'c- c» c, c, ~c7~ ~cX ~cX XX^ ~~c7
■ " I ...:-," '.-
C,-C,-C
... '. 31.6 28.0It
QH„ (^-CcC.-C-C-CjX^ 13.7 22 7 31 7'
XX7^^Q-OrQ-Q-C, ._ 22.7 27.9 41.9 20 8 14 3
C,-C,-C
a-C-C <= 5 jj 4 29 4 36 g ]g yC
1 C.-C.-C-C - .19.2 34,0__. JC,H,f Q-C,-C.-C_-C-C-C X~^ ~I3XT~ 22.6 32.0
?.' ; -XX - :; "-
Q-C,-C.-C«-C
4
-C,
- <_" 22.4 28. -1 .' 38.9
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C - ■_: . . . :■..:■■-.■ . I - .---;"
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Q-Ci-C,-C,-C
4
-C,
Cj _ 10.9 29.5- -34.3
#':'■;" "c c, "-""■;_■ '.--■'">■--.■ -= 11 '" -""." 20.0-.- .. G-Cj-Ca-Q-Q i* " 17.7 31.9 40.6C .... C .., -■_,: ■ . . ..-A :.. .I I .. ■.■ -..-. . -C-C.-C-C-C /O. 22.7 25 7 49
Tahle I. (continued)TMS = 0,
CS,
= +192.8Chemical shift
Identification Ci Ca Ct G C 4
C,
G G Cf
G-Ca-G-C.-C,
29.5 30.6 47.3 18.1 15.1I . .
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■
..
■
C
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G . "' "-.'.. " " -G-G-C-OC 7.7 33.4 32.3 25.6
Ic . ".... . . "■■■■' X. ..'CC . ■ " . . .' ■" '.' '' ■ " :
G-G-G-G 27.0 32.7 37.9 17.7I "■""-"■.
"\^~—V -■■■"" " -' : .■ X ■
G-Ca-G-C-C) 11 10.5- 25.2 42.4) Ijc^-r7■
■■"■.- ..;CaH„ (^Cj^G^a^ajC-C^^l^ / 13.6 _ 22.7 32.1 29.4
" G-CajG-C.-G-Ca-C,
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/522.4 28.1 39.3 27.2. 32.4 22.8 13.8
<V^^QIGjCa::G:C^c^_^--Vy 11.3-: 29.7 34.7 36.5 29.7 23.3 14.1 19.3-
-—— *-"* ~~~^ --.
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- C
G-Ca-C,-C
4-C-CrC-A /$ 14.1 20.2 39.5 32.3 .. 19.3
A CC, X"~~^ -- \T % '-',-■ -_X^ c^.-CizC'-CX-'^- 20 ° 328 X 38.5 36.7 . 20.7 Xl 15.1 , /""'
( ,-'' c g \ ... .I _______ f I ' 22.2-.
V_ c, -G G
C,
G G"X 23.2 25.4 46.6 32.1 29.9 11.0 19.0 j
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XCr^C^-C-CX fC 22.4 28.4 36.9 - . ".';
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- 25.8 38.5 13.8( G-C,-G-C-C^C Jy) n8
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......j G-C,-Ca-Ca-Ca-C, -. 29.2 30.1 44.1 27.0 23.7 .13.9
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'■■-G-G-G-G-Ca-G 8.1 34.3 32.8 44.3 17.3 14.8 26.5
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17.1 35.1 34.9 32.6 7.9 23.3 .V -. .-. .: '7' - " i "
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C c -.":-. : . ■ . X . ■- .; :J
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G-C,-C-C-
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"■-■""..i C C - „ . .f
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'■ Continued
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" Table I. (canft-n»^ITSIS =0- cs» T ChcmicaljhilL i
-,- _ n Cb>, = x»'— . . r_ —r— r. I
■
.TMS-».«« chcmicaUhirt - c, <- I"
__ —ca cr a . ;~cT~~^ -";." j " I %
" 40 6 35.4 20.0 14.1 " », '
G-C,^^' .26 11.8 Xr- C-C ' ■■ , ,„ , 47.6 22.0 . I 1
f/- - * 19.0 29.1G-C.Cr^f* .... 23 2 " .
. * . 7.5 30.6 34.8 23.2 ,-c.-c-c . ...... J i
C?q6- - » I ,\ .
'""'"« 0 29.4 29-° .. I .»C C-C-C^/r^-8 " 22 7 13.6 I ,r-CXXXX-C^ ,29 7 32.0 22.7 _._. [
GH,.
Cl ,q 2 27-4 2V X __— |C ,- 0/)??3 28 ° _—- " „r 19.0 r
V - c.iaii^S£_2_^ 269 a «.'.»"' j,
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30, B, ,3, .»CC. 20.1 „.," 340
„. c,iX,cc— " w9 , ,4.0 .*■« . ;
C C. 22.1 3 47 .0 30.2 . . I ' -oW^o "'l ; '
344 34, *-i ■""»: 19 °
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"" " C C« 22 -3 98 4 36.5 34.4 ' . .. \
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.| l r r 22.5 .. 28 -4 ... .. '.......;. .'X..;.. I.C C ■"''"■ ' -78 1 39.5 252
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;. Ci-Ca-Ca-Ca^^^ 31 .9 JJ-' J'.J \XC. C 10-9 »■$ 32.0 44.5 I ;
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a 23.7 1 3-' ?
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8 °' - C■""- X '"'-
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s 27.0 f<," X »■' ""'3 - 448 -C 257 23.S 15 - 5 |„
■-.■'.
CC,
C .7.8 36.2 «.9 ■ ».7i 1 I 70 0 ii-'* I
< r- -A -Ca-C«-Cs-C« . - 11 2 21.9 l
"" "'..<? j:^i-xx-:x,9. 3,.0 »""
3i - .. -re--. A
-■"" G-cyc.-c«-crC.^.. ..^.^. 1,.
PW .CX. X 28. 9 22.5 :."■'"""""■"/';JV X C. V
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29 3 30.1 .42-0, .. - . . CorJinued
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\\ GUST 1971