Download 1P18 IR spectroscopic investigation on intermolecular proton

1P18 IR spectroscopic investigation on intermolecular proton transfer
reactions in ionized diols
(Tohoku Univ.) 〇Yoshiyuki Matsuda, Ayumu Matsuura, Asuka Fujii
[Introduction]
Acidity enhancements of cationic OH and NH bonds have been demonstrated for
cationic clusters of phenol, aniline, water, ammonia, alcohols, and so on, so far.
Recently, high
acidities of cationic CH bonds have also been clarified for alkanes, alcohols, ethers, and amines,
although their neutral CH bonds are normally aprotic.[1] These findings raise the question which is
more acidic in cationic states, OH (and NH) or CH.
To compare acidities of cationic CH and OH bonds, we have studied an ionization-induced
proton transfer of ethylene glycol and propanediol, both of which have CH bonds and two OH bonds.
We have carried out the IR spectroscopy of their neutrals and cations to investigate the isomerization
involving the proton transfer in the ionization processes.
We discuss their isomerization dynamics
upon ionization with the IR spectroscopic results and the reaction path search calculations by use of
the Global Reaction Route Mapping (GRRM) [2] methods.
Based on these results, the comparisons
of acidities of cationic OH and CH are discussed.
[Experiments and Calculations]
IR spectroscopies of neutral and cationic diols were performed by
IR predissociation spectroscopy with monitoring the ion intensities through the vacuum-ultraviolet
photoionization by use of a time-of-flight mass spectrometers.[3]
performed at the PBE1PBE/6-31+G* level.
The GRRM [2] searches were
The obtained minimum and transition state structures
were re-optimized at the B97X-D/6-311++G(3df,3pd) level.
[Results and Discussion]
Fig.1(a) shows the IR spectrum of cationic ethylene glycol.
In addition
to the OH stretch at 3600 m-1 and CH stretches around 3000
cm-1, a broad feature is observed from 3200 cm-1 to the lower
frequency region.
This broad feature is assigned to the
H-bonded OH stretch of the most stable structure depicted in
Fig.1(b).
This structure is formed through the migration of
the water molecule which is generated by proton transfer from
CH to OH. This isomerization process is supported by the IR
spectroscopic result of the deuterated ethylene glycol and the
GRRM reaction path search calculation.
This isomerization
pathway implies the proton transfer from CH is more favorable
in ionized ethylene glycol.
Fig.1 (a) The observed IR spectrum
[References][1] Matsuda et al., JPCA, 119, 4885(2015). [2] Ohno
of cationic ethylene glycol and (b) its
and Maeda, CPL, 384, 277 (2004). [3] Matsuda et al., PCCP. 16, 9619
most stable structure optimized at the
(2014).
B97X-D/6-311++G(3df,3pd) level.