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CONFORMATIONAL TRANSFORMATION

OF FIVE-MEMBERED RINGS:

THE GAS PHASE STRUCTURES OF

2-METHYLTETRAHYDROFURANVinh Van

22. June 2015

CONFORMATIONAL TRANSFORMATION OF FIVE-MEMBERED RINGS: THE GAS PHASE STRUCTURES OF 2-METHYLTETRAHYDROFURAN

2-methyltetrahydrofuran (2-MeTHF): Green Chemistry

1

[1] V. Pace, P. Hoyos, L. Castoldi, P. Domínguez de María, A. R. Alcántara, ChemSusChem 5 (2012), 1369 – 1379.[2] D. F. Aycock, Org. Process Res. Dev. 11 (2007),156 – 159.[3] M. Smoleń, M. Kędziorek, K. Grela, Catalysis Communications 44 (2014), 80 – 84.[3b] (c) www.fb.com/effe.fineart Graphical abstract of [3]. [4] Z.-Q. Duan, F. Hu, J. Biotechnol. 163 (2013), 45 – 49.

• biofuel component derived from renewable resources [1]

• promising environmentally friendly solvent

• evaluated in various fields like

• organometallics [2]

• metathesis [3]

• biosynthesis [4]

way to more eco-friendly syntheses

[3b]

2-MeTHF


Five-membered rings

2


Five-membered rings

2


Five-membered rings

3

twist envelope

two typical ring structures

prototype: cyclopentane

envelope fold


• stable twists

• most stable conformer: same tilt direction

• envelope transition states

Five-membered rings

4

[1] V. Van, C. Dindic, H.V.L. Nguyen, and W. Stahl, ChemPhysChem 16, 291–294 (2015). [2] L. Margulès, M E. Sanz, S. Kassi, D. Petitprez, G. Wlodarczak, J. C. López, J. E. Boggs, Chemical Physics 263 (2001), 1, 19−31. [3] J.L. Alonso, J. C. López, and R. M. Villamañán, J. Mol. Spectrosc. 126 (1987), 348−355.[4] H. Mouhib, V. Van and W. Stahl, J. Phys. Chem. A 117 (2013), 6652−6656.

[2] [3]

[4][1]


2-Methyltetrahydrofuran (2-MeTHF)

twist

envelope

5


MTH F Conformational analysis

6

MP2/6-311++G(d,p)


I0.0 kJ∙ mol─1

Conformational analysis

6

below

ring plane

above

II4.4 kJ∙ mol─1


Calculated molecular parameters

7

= −0.624

conformer I

conf.A

[GHz]B

[GHz]C

[GHz]μa [D]

μb [D]

μc

[D]E rel

[kJ∙mol−1]I 6.649 3.172 2.367 −0.69 1.60 0.63 0.00II 5.207 3.624 2.922 −0.26 1.76 0.80 4.36

MP2/6-311++G(d,p)


Intramolecular conversion

8

twist

envelope

MP2/6-311++G(d,p)


Measurements

9

Molecular beam Fourier transform microwave spectrometer (frequency range 2 − 26.5 GHz)

scan-mode high-resolution mode

step width: 250 kHz instrumental line width: 2 kHz

co-added decays / step: 50


Assignments

10


Assignments

11

A [GHz]

B [GHz]

C [GHz]

exp. 6.591 3.170 2.367

calc. 6.649 3.172 2.367

MP2/6-311++G(d,p)


Molecular parameters fitted with the XIAM program

12

Parametera Unit Fit I (J ≤ 15) Fit II Fit III (J ≤ 6) MP2/6-311++G(d,p)

A GHz 6.59156823(22) 6.59156821(25) 6.59156814(18) 6.6489

B GHz 3.170370175(84) 3.17036995(14) 3.170370550(94) 3.1721

C GHz 2.367116054(88) 2.36711645(14) 2.36711598(11) 2.3673

J kHz 0.3312(13) 0.3340(21) 0.3368(20) 0.257

JK kHz 0.0641(35) 0.0822(45) 0.0703(58) 0.761

K kHz 2.855(20) 2.756(21) 2.787(14) 0.849

J kHz 0.05881(44) 0.05533(36) 0.06016(89) 0.057

K kHz 0.5322(69) 0.5516(59) 0.580(10) 0.561

HJK Hz −0.788(96)

HKJ Hz 2.83(35)

hJK Hz 0.331(46)

hK Hz −2.84(55)

kHz 2.2 3.6 1.4

N 111 111 72 a Principal axis system, Watson’s A reduction in Ir representation


Methyl internal rotation

13

Only 8 decays were co-added!!!

V3 (calc) = 1142 cm─1

130 decays were co-added.


Methyl internal rotation

14

Parameter Unit Fit I Fit IV (Int.Rot.)A GHz 6.59156823(22) 6.59156543(31)B GHz 3.170370175(84) 3.17040277(28)C GHz 2.367116054(88) 2.36708337(27)J kHz 0.3312(13) 0.3303(20)JK kHz 0.0641(35) 0.0706(50)K kHz 2.855(20) 2.688(18)J kHz 0.05881(44) 0.05615(38)K kHz 0.5322(69) 0.5336(61)HJK Hz −0.788(96) −0.111(16)HKJ Hz 2.83(35)hJK Hz 0.331(46)hK Hz −2.84(55)V3 cm−1 1057(14)Iα uÅ2 3.1986(fixed)

∠(i,a) ° 17.16(fixed)∠(i,b) ° 88.75(fixed)∠(i,c) ° 72.89(fixed)Dpi2J kHz 0.0178(48)Dpi2− kHz 0.00273(52) kHz 2.2 3.7N 111 138


Isotopologues

15

conformer I

frequency [MHz]

unassigned


“Noises?“

15

conformer I

frequency [MHz]

unassigned


13C or conformer II?

16

13C isotopologue in natural abundance of 1.1 %. 97 decays were co-added.


IsotopologueA

[GHz]B

[GHz]C

[GHz]parent 6.649 3.172 2.36713C(9) 6.648 3.082 2.31713C(5) 6.607 3.125 2.33613C(1) 6.590 3.136 2.34013C(4) 6.637 3.159 2.362

13C(14) 6.518 3.172 2.35118O 6.451 3.171 2.342

Assignments of the isotopologues

17


Molecular parameters fitted with the XIAM program

18

Parameter Unit 13C(1) 13C(4) 13C(5) 13C(9) 13C(14)A GHz 6.53423752(71) 6.57970964(61) 6.55107431(70) 6.59028755(61) 6.46187441(69)B GHz 3.13465551(41) 3.15713442(33) 3.12372913(38) 3.08086383(37) 3.17000430(43)C GHz 2.34012997(37) 2.36130876(29) 2.33611689(36) 2.31701145(35) 2.34994423(31)J kHz 0.3235(76) 0.3318(69) 0.329(12) 0.3143(72) 0.3355(82)K kHz 2.610(59) 3.021(51) 2.696(55) 2.997(50) 2.781(53)J kHz 0.0496(44) 0.0665(30) 0.0553(27) 0.0513(48) 0.0663(35)K kHz 0.709(43) 0.596(26) 0.544(27) 0.617(56) 0.662(39) kHz 2.4 2.3 2.8 3.0 2.3N 30 33 37 37 31


Search of 18O-isotopologue

19

18O isotopologue in natural abundance: 0.2 %.

6 Scans of 10 - 15 MHz

Parameter broadband scan for 13C isotopologues

broadband scan for 18O isotopologue

step width 250 kHz 200 kHz

decays / step 50 750time 50 MHz / hour 2 MHz / hour



19

18O isotopologue in natural abundance: 0.2 %.

6 Scans of 10 - 15 MHz

Parameter broadband scan for 13C isotopologues

broadband scan for 18O isotopologue

step width 250 kHz 200 kHz

decays / step 50 750time 50 MHz / hour 2 MHz / hour



20

303 202 noise



20

303 202 750 FPDs 5000 FPDs


Intensities of the isotopologues

21


Intensities of the isotopologues

22

1000 FPDs 5000 FPDs2 FPDs !


18O-Molecular parameters fitted with the XIAM program

23

Parameter Unit parent species (Fit III) all 13C-isotopologues 18O(8)-isotopologue

A GHz 6.59156814(18) 6.462 - 6.580 6.3962301(30)

B GHz 3.170370550(94) 3.081 - 3.170 3.16966061(63)

C GHz 2.36711598(11) 2.317 - 2.361 2.34229427(70)

J kHz 0.3368(20) 0.314 - 0.336 0.332(29)

JK kHz 0.0703(58) - -

K kHz 2.787(14) 2.610 - 3.021 2.53(53)

J kHz 0.06016(89) 0.0496 - 0.0665 0.06016(fixed)

K kHz 0.580(10) 0.544 - 0.709 0.580(fixed) kHz 1.4 2.2 - 3.0 3.0N 72 30 - 37 14


Microwave structure determination using Kraitchman‘s equation

24

|a|/Å |b|/Å |c|/ÅC(1) 1.34277(90) 0.8240(15) 0.118(11)C(4) 0.7290(17) 0.050(24) 0.3774(32)C(5) 1.54132(78) 0.6932(18) 0.104(12)O(8) 0.104(12) 1.0794(12) 0.1748(69)C(9) 2.15737(56) 0.019(63) 0.1231(98)

C(14) 0.1402(86) 1.24634(97) 0.039(31)

blue: experimental atom positionsgrey: MP2/6-311++G(d,p)


Microwave structure determination using Kraitchman‘s equation

25

blue: experimental atom positionsgrey: MP2/6-311++G(d,p)

exp. / ° calc. / °ring plane

φ −6.48(21) −3.66envelope fold

γ' 135.715(48) 137.46

γ 139.950(54) 139.90

Place to Be – RWTH Start-Up

Acknowledgements

Prof. Dr. Wolfgang StahlRWTH Aachen University, Germany

Dr. Ha Vinh Lam NguyenLaboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), UPEC, France

JARA-HPC

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