th  - 1988 - 51st ENC Conference

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DIRECT OBSERVATION OF LONG RANGE HETERONUCLE~ SPLIETINGS IN
• PROTON 2DJ SPECTRA: T. K. Pratum, P. K. Hammen* and N. H.
] Andersen, University of Washington, Seattle WA 98195
Pr0ton-detected heteronuclear 2DJ-resolved experiments have been designed
a/_lo~ring the observation of long range heteronuclear couplings (nJcH). Placement
of a 180 ~ carbon pulse at the midpoint of the hon~nuclear 2DJ evolution period pr~ah~ces
a signal n~dulated by both heteronuclear and hamonuclear coupling. Selective
detection of protons ~rith long range coupling to 13C nuclei surmounts the inherent
d C~p'ul c r~l~Be difficulty encount~d with proton dete.ct.ion. For this selection the
se at the nlidpoint of t I is n~Ddulated or an additlona_l n~ulated 180 n C_I
pulse is placed either at the end of t I or at the beginning but a fixed, (2 JCH ) ,
delay a~ter the initial proton 90 ° pulse. %~nese lead to differs_noes in the signal
detected, and corLsequently in data presentation. Of them the most useful sequence
, ,2 "* I I "'*
IH I I Acq(e.)
In this case, a 45 ° projection of the 2D data matrix elindnates proton J couplings
preser~ring the long range heteronuclear couplings. A~litude reduction of the mod-
ulated 13C pulse, nmk/_ng it sendselective for a desired sl~ect-ral region, pr~)vides
another advantage. It elind_nates all but the couplings to the selected carbons
which is beneficial when several couplings exist with nearly identical n~gnitude.
%~nese metheds have been developed ~sing ar~m~itic an~o acids as test systems
• ~rith selective 13 C edifying in the carbonyl region. %~ne experiment has been extend-
ed to l~=-ptides where it provides a means for assigning diastereotopic methylene
protons and deter~dzling the side cha/in dihedral angles.
141 I BRANCH LOCATION STUDIED BY SOLVENT SWELLING AND SOLID
STATE NMR IN ISOTOPICALLY ENRICHED ETHYLENE-I-BUTENE COPOLYHERS:
D. HcFaddin, Queen's University, Kingston, Ontario, Canada. K7L 3N6
Homogenous ethylene-l-butene copolymers (isotoplcally enriched
at the methyl group) have been studied by solid state NHR, as a
function of crystallization conditions and comonomer content. Two
enviror~nents are seen for the branches Ln all cases.
Ln the solution crystallized samples the methyl region of the
spectrum is characterized by two broad overlapping peaks. However,
the addition of excess solvent (carbon tetrachloride) causes an
increase in the mobility of the amorphous chains and improved
resolution in the methyl region of the spectrum. The solvent does
not penetrate the crystalline regions of the polymer and therefore
only effects the amorphous branches of the sample.
In a 0.2 tool% sample (crystallized from the melt)
approximately 18% of the branches reside in a restricted region,
while 37% of the branches exist in a crystalline-like (non-swollen)
region in the solution crystallized polymer. In a 2.5 mol% sample
approx~ately 12% (melt crystallized) and 22% (solution
crystallized) of the total branches exist in this crystalline-like
(non-swollen) region of the polymer. These sidechains are probably
located in a defective crystalline overlayer.
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