Electronic Supporting Information (ESI)

Unraveling the Protonation Site of Oxazole and Solvation with Hydrophobic

Ligands by Infrared Photodissociation Spectroscopy

Kuntal Chatterjee and Otto Dopfer* Institut für Optik und Atomare Physik, TU Berlin, Hardenbergstr. 36, 10623 Berlin, Germany.

* Corresponding author: dopfer@physik.tu-berlin.de

Figure S1. Optimized structures of various H+Ox isomers calculated at the B3LYP-D3/aug-cc-pVTZ

level. Relative energies and free energies (E0, G0) and bond lengths are given in kJ mol-1 and Å,

respectively.

Figure S2. Linear IR absorption spectra of neutral Ox and various H+Ox isomers obtained at the

B3LYP-D3/aug-cc-pVTZ level.

Figure S3. NBO atomic charge distributions (in e) of Ox, H+Ox, and H+Ox-L(H) dimers with L=Ar and

N2 obtained at the B3LYP-D3/aug-cc-pVTZ level.

Figure S4. Orbital interaction between the σ* orbital of the N-H bond and the lone pair of L involved in

the NH…L H-bond in the H+Ox-L1,2 clusters (L=Ar and N2) obtained from the NBO analysis at the

B3LYP-D3/aug-cc-pVTZ level. The numbers are E(2) values in kJ mol-1.

Figure S5. Visualization of the NCI analysis of the NH…L H-bond in the H+Ox-L(H) dimers (L=Ar and

N2) calculated at the B3LYP-D3/aug-cc-pVTZ level. The numbers are ρ* values in a.u.

Figure S6. Optimized structures of H+Ox and various H+Ox-N2 isomers calculated at the B3LYP-

D3/aug-cc-pVTZ level. Binding energies (D0) and bond lengths are given in cm-1 and Å, respectively.

Numbers in parentheses correspond to relative energies and free energies in cm-1 (E0, G0).

Figure S7. Comparison of linear IR absorption spectra of various H+Ox-N2 isomers obtained at the

B3LYP-D3/aug-cc-pVTZ level to the measured IRPD spectrum.

Figure S8. Comparison of linear IR absorption spectra of Ar/N2-bound O- and C-protmers calculated

at the B3LYP-D3/aug-cc-pVTZ level to the measured IRPD spectra.

Figure S9. Optimized structures of two H+Ox-(N2)3 isomers calculated at the B3LYP-D3/aug-cc-pVTZ

level. Binding energies (D0) and bond lengths are given in cm-1 and Å, respectively. Numbers in

parentheses correspond to relative energies and free energies in cm-1 (E0, G0).

Figure S10. Optimized structure of the H+Ox-(N2)4(2H/2π) isomer along with its linear IR absorption

spectrum calculated at the B3LYP-D3/aug-cc-pVTZ level. The total binding energy (D0) and bond

lengths are given in cm-1 and Å, respectively.

Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics.This journal is © the Owner Societies 2019

Figure S1

Figure S2

Figure S3

Figure S4

17.3 42.2

41.1

2.7

29.8

Figure S5

-ρ* = 0.01278 -ρ* = 0.02205

Figure S6

Figure S7

Figure S8

Figure S9

Figure S10

Table S1. Experimental and theoretical (B3LYP-D3/aug-cc-pVTZ) structural parameters of neutral Ox

and respective changes upon N-protonation.

a A. Kumar, J. Sheridan and O. L. Stiefvater, Z. Naturforsch. A, 1978, 33, 145–152.

structural parameters Ox H+Ox

calc expa Calc

rO1C2 1.3556 1.357 1.3056

rC2N3 1.2879 1.291 1.3134

rN3C4 1.3899 1.395 1.3921

rC4C5 1.3497 1.352 1.3439

rC5O1 1.3693 1.369 1.3777

rC2H2 1.0763 1.075 1.0778

rC4H4 1.0737 1.075 1.0748

rC5H5 1.0754 1.073 1.0745

rN3H3 1.0125

< (C5O1C2) 104.2 103.9 107.9

< (O1C2N3) 114.5 114.9 109.8

< (C2N3C4) 104.4 103.9 108.8

< (N3C4C5) 109.0 109.0 105.3

< (C4C5O1) 107.9 108.1 108.2

< (O1C2H2) 116.9 117.0 121.6

< (N3C4H4) 122.0 121.8 122.9

< (O1C5H5) 117.0 116.8 117.1

Cartesian coordinates of relevant optimized structures

Ox

C 0.00000000 1.10171400 0.00000000 C -0.75239200 -0.87674700 0.00000000 C 0.59443600 -0.96493500 0.00000000 H 0.16665200 2.16500200 0.00000000 H -1.48218800 -1.66666300 0.00000000 H 1.30418100 -1.77054800 0.00000000 O 1.09895700 0.30802400 0.00000000 N -1.11893800 0.46397500 0.00000000

H+Ox(N)

C -1.06446800 0.33785000 0.00000000 C 1.13523900 0.30147600 0.00000000 C 0.67439900 -0.96092300 0.00000000 H -2.10313100 0.62547400 0.00000000 H 2.13331500 0.70022400 0.00000000 H 1.13309000 -1.93257100 0.00000000 O -0.70261500 -0.91663000 0.00000000 N 0.00000000 1.10713900 0.00000000 H -0.01337700 2.11952200 0.00000000

H+Ox(C2)

C 0.63544400 0.96535400 0.00000000 C -1.16534700 -0.27721900 0.00000000 C 0.00000000 -1.15407400 0.00000000 H 1.06460100 1.41452200 0.90006100 H -2.20181100 -0.58252800 0.00000000 H 0.07023400 -2.23684900 0.00000000 O 1.06468500 -0.47650900 0.00000000 N -0.76224100 0.94257700 0.00000000 H 1.06460100 1.41452200 -0.90006100

H+Ox(C4)

C 0.68472500 0.96108300 0.00000000 C -1.15404800 -0.21628400 0.00000000 C 0.00000000 -1.13599200 0.00000000 H 1.53179100 1.62927600 0.00000000 H -1.80156900 -0.37215100 0.87431100 H 0.02924000 -2.22116300 0.00000000 O 1.08456200 -0.49986500 0.00000000 N -0.54549300 1.09746800 0.00000000 H -1.80156900 -0.37215100 -0.87431100

H+Ox(C5)

C 0.00000000 -1.11853300 0.00000000 C 0.82205900 0.81773600 0.00000000 C -0.64676900 0.97513500 0.00000000 H -0.08693000 -2.19905700 0.00000000 H 1.54508800 1.62464800 0.00000000 H -1.05432800 1.46279800 0.89106600 O -1.07461900 -0.41555000 0.00000000 N 1.17081500 -0.43897400 0.00000000 H -1.05432800 1.46279800 -0.89106600

H+Ox(O)

C 1.18136400 -0.12553100 0.00379800 C -0.88998300 -0.79895100 0.00944600 C -1.05268300 0.52247900 0.00123900 H 2.23068100 0.11938100 -0.01518000 H -1.65267400 -1.55843700 0.01056300 H -1.87192800 1.21898600 -0.01373600 O 0.26050700 1.08254000 -0.05544800 N 0.47432600 -1.14180800 0.00815300 H 0.45739400 1.96442500 0.31797600

H+Ox-Ar(H)

C 1.08941700 1.11118400 0.00000000 C -1.10532800 1.22455200 0.00000000 C -0.60165100 2.47064400 0.00000000 H 2.11712800 0.78731700 0.00000000 H -2.11649600 0.86064700 0.00000000 H -1.02644000 3.45747500 0.00000000 O 0.77282800 2.37892200 0.00000000 N 0.00000000 0.37955900 0.00000000 H -0.02229400 -0.63607000 0.00000000 Ar -0.07939700 -3.05533000 0.00000000

H+Ox-Ar(π)

C -0.89530900 -0.91024400 -0.69174400 C -1.30180700 0.36602800 1.05246700 C -1.24362100 1.13266800 -0.04962000 H -0.69442900 -1.73295000 -1.35779400 H -1.47505700 0.60778100 2.08512700 H -1.34766900 2.18400700 -0.24454200 O -0.99156300 0.31581400 -1.12950100 N -1.07791300 -0.93340500 0.60832600 H -1.04719900 -1.76434900 1.18544400 Ar 2.26037100 0.06567300 0.06904900

H+Ox-Ar2(2H)

C 0.02393700 -1.82081300 0.00000000 C 1.92267400 -0.71412800 0.00000000 C 2.18375200 -2.03265200 0.00000000 H -1.01425200 -2.10758800 0.00000000 H 2.56718500 0.14558200 0.00000000 H 3.07938800 -2.62589900 0.00000000 O 0.98314600 -2.70875600 0.00000000 N 0.53588000 -0.61315900 0.00000000 H 0.00000000 0.24799700 0.00000000 Ar 0.41741100 2.78954100 0.00000000 Ar -2.69690200 0.41643800 0.00000000

H+Ox-Ar2(H/π)

C 0.53269900 -0.87033000 1.08612500 C 0.48909100 -1.27165100 -1.07337100 C 1.70372000 -1.58767100 -0.59282000 H 0.29747600 -0.59221800 2.09988300 H 0.07600600 -1.32073800 -2.06409600 H 2.60926700 -1.97374900 -1.02278400 O 1.71058900 -1.33223300 0.76039200 N -0.23562100 -0.81926000 0.02390000 H -1.19586000 -0.48921900 0.01289200 Ar -3.47009500 0.34751900 -0.00854700 Ar 1.79368900 2.04951000 -0.09122700

H+Ox-Ar2(2π)

C -0.87999000 -0.05863000 0.00000000 C 1.13263200 0.82584400 0.00000000 C 1.24064100 -0.51347900 0.00000000 H -1.94338000 -0.22990700 0.00000000 H 1.87340400 1.60418700 0.00000000 H 2.06298300 -1.20452000 0.00000000 O -0.02834400 -1.04770400 0.00000000 N -0.23389400 1.08407400 0.00000000 H -0.66850600 1.99785300 0.00000000 Ar -0.23389400 -0.08047000 3.33161100 Ar -0.23389400 -0.08047000 -3.33161100

H+Ox-N2(H)

C 1.06135700 -0.95359700 0.00000000 C -1.13319500 -0.98989300 0.00000000 C -0.67482600 -2.25344200 0.00000000 H 2.10000000 -0.66729900 0.00000000 H -2.13122100 -0.59158300 0.00000000 H -1.13454600 -3.22442000 0.00000000 O 0.70165400 -2.21074100 0.00000000 N 0.00000000 -0.18303500 0.00000000 H 0.01248300 0.83771400 0.00000000 N 0.00740800 2.86890300 0.00000000 N -0.00454600 3.95886200 0.00000000

H+Ox-N2(π)

C -0.84563200 -0.97172600 -0.57768700 C -1.17080300 0.52897900 0.99522500 C -1.03282700 1.15291300 -0.18697300 H -0.70425400 -1.88080200 -1.13805800 H -1.33966200 0.90436800 1.98784600 H -1.04807600 2.17884700 -0.50508600 O -0.83531800 0.19720600 -1.15786800 N -1.05044000 -0.82702100 0.71092500 H -1.09736000 -1.58382200 1.38107300 N 2.07257400 -0.07404800 0.06169100 N 3.14464800 0.12146400 0.10649600

H+Ox-(N2)2(2H)

C -0.61364800 1.48807300 0.00000000 C -2.11549600 -0.11233500 0.00000000 C -2.74381900 1.07579600 0.00000000 H 0.29817200 2.05951000 0.00000000 H -2.49014500 -1.11932000 0.00000000 H -3.77178500 1.38756000 0.00000000 O -1.78708100 2.06651400 0.00000000 N -0.75717200 0.18510000 0.00000000 H 0.00000000 -0.49582400 0.00000000 N 2.47353600 0.46366500 0.00000000 N 3.56267200 0.40824500 0.00000000 N 0.89548000 -2.41059600 0.00000000 N 1.41093800 -3.37116200 0.00000000

H+Ox-(N2)2(H/π)

C 0.38742100 -0.79879200 1.08033900 C 0.33600900 -1.12119000 -1.08843100 C 1.54315800 -1.48229800 -0.62049900 H 0.15866000 -0.55255200 2.10343900 H -0.07651400 -1.12676100 -2.08045400 H 2.43882700 -1.87482000 -1.06474600 O 1.55495300 -1.27775000 0.74022600 N -0.38024300 -0.69270600 0.02282100 H -1.33761800 -0.34116100 0.02312200 N 1.75483800 1.80068200 0.00798600 N 2.27094700 2.74638900 -0.16183500 N -3.25447300 0.35497200 -0.00385000 N -4.27999800 0.72365900 -0.02678300

H+Ox-N2(2π)

C -0.85933700 0.44145800 0.00000000 C 1.33267900 0.30263800 0.00000000 C 0.81249300 -0.93641700 0.00000000 H -1.88192600 0.77869100 0.00000000 H 2.34851500 0.65253600 0.00000000 H 1.22600100 -1.92762700 0.00000000 O -0.55872500 -0.82787600 0.00000000 N 0.23897400 1.15951800 0.00000000 H 0.27260900 2.17042400 0.00000000 N -0.24583000 0.01586600 3.03932500 N -0.24583000 -0.15970300 4.11577500 N -0.24583000 0.01586600 -3.03932500 N -0.24583000 -0.15970300 -4.11577500

H+Ox-(N2)3(2H/π)

C -0.78083200 0.10903100 -1.23470700 C -1.08665100 -1.68713300 -0.01411300 C -2.22759100 -1.40135000 -0.66450800 H -0.37732000 0.97820700 -1.72323900 H -0.83287100 -2.47408900 0.67167600 H -3.20422100 -1.84605800 -0.70776800 O -2.01552900 -0.27594200 -1.42770100 N -0.18213400 -0.70683200 -0.40230800 H 0.78072700 -0.62720100 -0.08337300 N 2.17582300 1.44149600 -0.96023400 N 3.04480600 2.09431300 -1.04951800 N 2.52936200 -1.17518700 0.99035600 N 3.45573300 -1.40952000 1.51506300 N -2.11438700 1.29649500 1.32796100 N -2.57658100 1.89543300 2.11357600

H+Ox-(N2)3(H/2π)

C -0.95395700 -0.35021600 0.00000000 C 1.22201100 -0.61185600 0.00000000 C 0.63502300 -1.82097500 0.00000000 H -1.95609200 0.04282800 0.00000000 H 2.25584700 -0.32001200 0.00000000 H 0.99293000 -2.83344900 0.00000000 O -0.72759700 -1.63681700 0.00000000 N 0.18033900 0.30625500 0.00000000 H 0.27250400 1.32108700 0.00000000 N -0.35944100 -0.81404600 3.04406300 N -0.35944100 -0.98213700 4.12170600 N -0.35944100 -0.81404600 -3.04406300 N -0.35944100 -0.98213700 -4.12170600 N 0.48474900 3.35734200 0.00000000 N 0.60655200 4.44053600 0.00000000

H+Ox-(N2)4(2H/2π)

C -0.75417300 -0.82214100 0.00000000 C 1.42690200 -1.03574600 0.00000000 C 0.86765800 -2.25790900 0.00000000 H -1.76190500 -0.44725800 0.00000000 H 2.45353200 -0.71995100 0.00000000 H 1.24811400 -3.26203700 0.00000000 O -0.49889500 -2.10399700 0.00000000 N 0.36514800 -0.14190900 0.00000000 H 0.44199600 0.87177800 0.00000000 N -1.79529500 2.26431200 0.00000000 N -2.41740800 3.15998100 0.00000000 N 1.45524400 2.74961700 0.00000000 N 1.91770200 3.73679600 0.00000000 N -0.15395100 -1.25545200 3.04407000 N -0.15395100 -1.25545200 -3.04407000 N -0.15395100 -1.40864400 4.12392000 N -0.15395100 -1.40864400 -4.12392000