CONFORMATIONS AND BARRIERS TO METHYL GROUP INTERNAL ROTATION IN TWO ASYMMETRIC ETHERS: PROPYL METHYL ETHER AND BUTYL METHYL ETHER. TC-06: June 19 th, 2012.

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CONFORMATIONS AND BARRIERS TO METHYL GROUP INTERNAL ROTATION IN TWO ASYMMETRIC ETHERS: PROPYL METHYL ETHER AND BUTYL METHYL ETHER. TC-06: June 19 th, Brittany E. Long*, Frank DeChirico ǂ, and Stephen A. Cooke ǂ * ǂ

Chirped Pulse Fourier Transform Microwave Spectrometer at Wesleyan 2

Novick Lab Picture 3

CP-FTMW 4  Based upon the work of Pate and coworkers 1  Uses a fast passage pulsing technique known as a “chirp”  8-18 GHz range with up to 4 GHz regions at a time  Directly digitized setup shown here  TC-04 for more detailed explanation Vacuum Chamber 1. G. G. Brown, B. C. Dian, K. O. Douglass, S. M. Geyer, B. H. Pate, J. Mol. Spectrosc. 238 (2006) 200.

MOLECULES 5

Motivation for Molecules To study internal rotation To study asymmetric aliphatic CHO ethers 6

Asymmetric Aliphatic CHO Ethers trans-ethyl methyl ether has been studied many different times in the past. M. Hayashi, et. al., J. Mol. Struct. 28 (1975) 147. K. Kobayashi, et. al., J. Mol. Spectrosc. 251 (2008) 301. U. Fuchs, et. al., Astrophys. J. Suppl. Ser. 144 (2003) 277. Plus several other paper not listed trans-trans isomer of propyl methyl ether has been studied H. Kato, et. al., J. Mol. Spectrosc. 80 (1980) 272. Isopropyl methyl ether has been studied J. Nakagawa, et. al., J. Mol. Struct. 112 (1984)

Trans-ethyl methyl ether 8 *only conformer ever observed

Trans-ethyl methyl ether parameters 1 Trans-ethyl methyl ether A (31) MHz B (4) MHz C (4) MHz ΔJΔJ -1.26(56)* kHz V 3 (OCH 3 )945 ± 2 cm -1 (893 cm -1 “after kinetic coupling taken into account”) I α (OCH 3 ) amu Å 2 V 3 (CCH 3 )1154 ± 9 cm -1 I α (CCH 3 ) amu Å 2 F GHz 9 1.M. Hayashi, et. al., J. Mol. Struct. 28 (1975) 147. *value was reported negative in paper

Relative Energies: Propyl methyl ether 10 Trans trans- propyl methyl ether Energy: 83 cm -1 higher Trans gauche-propyl methyl ether Energy: 0 cm -1 Potential third conformer-not observed Energy: 456 cm -1 higher MP2/6-311G++(2d,2p)

Trans trans-propyl methyl ether 11 τ 1 = 179.6˚ τ 2 =179.4˚

Trans trans- propyl methyl ether parameters 1 Trans trans-propyl methyl ether A (14) MHz B (1) MHz C (1) MHz ΔJΔJ 3.5(10) kHz V 3 (OCH 3 )“searches for spectra due to the excited state of the OCH 3 torsion were unsuccessful.” I α (OCH 3 )-- V 3 (CCH 3 )1154 ± 20 cm -1 I α (CCH 3 ) amu Å 2 FNot reported H. Kato, et. al., J. Mol. Spectrosc. 80 (1980) 272.

Trans gauche-propyl methyl ether 13 a c b C1C1 C4C4 C3C3 C2C2 τ1 τ1 τ2 τ2

Trans gauche-propyl methyl ether 14 C2H5C2H5 H CH 3 H H H OCH 3 CH 3 H H τ 1 = 179.6˚ τ 2 =62.9˚ MP2/6-311G++(2d,2p) IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN doi: /goldbook.doi: /goldbook transgauche

Microwave Spectrum for Propyl Methyl Ether

Trans gauche-propyl methyl ether parameters State 1State 2 A /MHz (15) (15) B /MHz (4) (4) C /MHz (4) (4) Δ J /kHz1.240(10)0.883(10) Δ JK /kHz-8.87(8)-8.73(8) δ J /kHz0.2218(15)0.2216(15) n25 RMS /kHz *preliminary fit

Problem for trans gauche-propyl methyl ether 17 PROBLEM Shots

Relative Energies: Butyl methyl ether 18 Trans trans trans- butyl methyl ether Energy: 130 cm -1 higher Trans gauche trans-butyl methyl ether Energy: 0 cm -1 MP2/6-311G++(2d,2p)

Trans gauche trans-butyl methyl ether 19 a c b C1C1 C4C4 C3C3 C2C2 C5C5 τ1 τ1 τ3 τ3 τ2 τ2

Trans gauche trans- butyl methyl ether 20 C2H5C2H5 H CH 3 H H H OCH 3 C2H5C2H5 H H CH 3 H CH 2 OCH 3 H H H MP2/ 6-311G++(2d,2p) τ 1 = 179.9˚ τ 2 = 62.5˚ τ 3 = 179.0˚ IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN doi: /goldbook.doi: /goldbook gauche trans

Microwave Spectrum for Butyl Methyl Ether 21

Trans gauche trans-butyl methyl ether parameters A StateE StateXIAM A /MHz (30) (30) (34) B /MHz (63) (67) (20) C /MHz (74) (77) (21) Δ J /kHz0.3063(72)0.2909(74)0.299(7) Δ JK /kHz-7.351(92)-7.383(78)-7.40(10) Δ K /kHz98.64(54)91.11(54)94.6(7) δ J /kHz0.0504(31)0.0500(30)0.0515(25) D a /MHz0.3870(48) n RMS /kHz V 3 /cm -1 (OCH 3 )780 ± 35 F /GHz I α /amu Å κ

Barrier Height Comparisons MoleculeV 3 (OCH 3 ) /cm -1 V 3 (CCH 3 ) /cm -1 Methyl C-O / Å Trans-ethyl methyl ether ± ± (6) Trans trans-propyl methyl ether 2 NA1154 ± (8) Isopropyl methyl ether ± 8NA1.416 Trans gauche- propyl methyl ether 4 UndeterminedNA1.416* Trans gauche trans- butyl methyl ether ± 35NA1.412* 23 1.M. Hayashi, et. al., J. Mol. Struct. 28 (1975) H. Kato, et. al., J. Mol. Spectrosc. 80 (1980) J. Nakagawa, et. al., J. Mol. Struct. 112 (1984) This work 5.This work * Bond angles from optimized MP2/6-311G++(2d,2p) calculations. Final structure not determined yet.

Conclusions Rotational constants and centrifugal distortion constants for trans gauche trans-butyl methyl ether have been determined for the first time. Work in progress for trans gauche-propyl methyl ether Barrier height to internal rotation for trans gauche trans- butyl methyl ether has been determined XIAM fit for trans gauche-propyl methyl ether to determine barrier height still a work in progress. Something unknown seems to be happening with the molecule Want to try ERHAM 24

Future Work 13 C for both butyl methyl and propyl methyl ethers Pentyl methyl and hexyl methyl ethers Laser ablation on lanthanide and actinide molecules. (Th, U, Lu, Nd) Chirp room temperature waveguide 25

Acknowledgements Novick, Pringle and Cooke Group Laboratory Funding from the NSF and US DOE 26

Trans trans- methyl propyl ether 27 C2H5C2H5 H CH 3 H τ 1 = 179.6˚ τ 2 =179.4˚MP2/6-311G++(2d,2p) IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN doi: /goldbook.doi: /goldbook CH 3 H OCH 3 H H H

Effective rotation-Coriolis Hamiltonian G.S. Grubbs II, et. al., “Methyl Group Internal Rotation and the Choice of Hamiltonian for the Rotational Spectrum of 1,1- Difluoroacetone,” J. Mol. Spectrosc. Submitted