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Investigating Restricted g gC‐N Bond Rotation
Ashley McDonald Robert Nelson Stacey A Stoffregen and Karl P PetersonAshley McDonald, Robert Nelson, Stacey A. Stoffregen, and Karl P. Peterson
MU3C Online Conference
b th thFebruary 5th‐7th, 2013
University of Wisconsin‐River Falls
AbstractWhile single bonds in organic molecules can often freely rotate, certain
molecules exhibit restricted rotation of their single bonds. The meta‐(A) and ortho‐(B) derivatives of anisidine, where X=OCH3 and Y=OH, were prepared. Spectroscopic analysis (1H NMR) of the synthesized materials suggests that theSpectroscopic analysis ( H NMR) of the synthesized materials suggests that the highlighted C‐N bond of B exhibits restricted rotation. Using computational chemistry methods, the barriers of rotation for both structures were calculated. A larger energy barrier to rotation was observed for B and is therefore supportive of the spectroscopic evidence for restricted rotation. To further investigateof the spectroscopic evidence for restricted rotation. To further investigate restricted rotation over a series of related molecules, a halogen (either F, Cl, Br, and I) atom is being placed on both derivatives at position X and a H atom at position Y. The structures are being synthesized and 1H NMR of the derivatives is being collected at various temperatures. The barrier to rotation is also beingbeing collected at various temperatures. The barrier to rotation is also being calculated for all structures.
C HSynthesis
Reaction A
NCH3
OH
H
H
OC H3
salicylamide meta anisidine
NCH3
O H
H
H
HH
H
H�
salicylamide meta‐anisidine HH
Reaction B
Compound A (X = CH3 and Y = OH)‐meta substituted
H
HNH
CH3
OO
HC H3Reaction B
HH
H
H H
O H
li l id h i idi
�
H Hsalicylamide ortho‐anisidine Compound B
(X = OCH3 and Y = OH)‐ortho substituted
1H NMR of Synthesized MaterialsS t i l i f d A d B h X OCH d Y• Spectroscopic analysis of compounds A and B, where X = OCH3 and Y = OH, yielded the expected signals for all hydrogen atoms in their structures with the exception of the CH2 hydrogen atoms.
F th 1H NMR t th th l (CH ) h d t f• From the 1H NMR spectrum, the methylene (CH2) hydrogen atoms of compound B (the ortho‐substituted ring), appear to be non‐equivalent, suggesting the presence of rotational restriction of the C‐N bond shown in boldbold.
• This same behavior was not observed for the methylene hydrogen atoms of compound A (the meta‐substituted ring).
HC H3
H
HNH H
CH 3
OO
HC H3
HH
H
H H
O HH
H
ortho‐ substitutedanisidine
meta‐ substitutedanisidine
H H
1H NMR of Compound A• Spectroscopic analysis of Compound A (‐meta substituted) yielded results
consistent with its structure
2H
3H
1H
8H
2H
3H
1H NMR of Compound B• Spectroscopic analysis of Compound B (‐ortho substituted) yielded
unexpected signals
3H 3H
1H8H
The methylene (CH2) hydrogen atoms of compound B, appear
b i l
1Ha/b1Ha/b
to be non‐equivalent
• The methylene H’s appear as non‐equivalent H’s in the spectrum of compound B, suggesting restricted rotation about N‐Ar bond.
• The infrared spectra of ortho‐ andThe infrared spectra of ortho and meta‐derivatives are nearly identical suggesting similar structuressuggesting similar structures.
Computational Analysis of Bond Rotation• Compounds A and B, where X=OCH3 and Y=OH, were optimized using
computational chemistry while varying the C‐N‐C‐C dihedral angle at fixed intervals.
• An energy plot was generated from these constrained optimizations.
• To further investigate restricted rotation, a halogen (either F, Cl, Br, and I) atom is being placed on both derivatives at position X and a H atom at g p pposition Y.
• The barrier to rotation is being calculated for all structures.
Computational Analysis
• Initially structures were optimized using a semi‐
Computational Analysis
empirical method with PC Spartan Student Edition v5.0.0
• Atomic coordinates generated used in subsequent constrained optimizations performed using GAMESS software at the B3LYP/6 31G levelsoftware at the B3LYP/6‐31G level
• The structures from these calculations were visualized using MacMolPltvisualized using MacMolPlt.
Computational Analysis
• The observance of a larger energy barrier to
Computational Analysis
rotation in the ortho‐ derivative would be supportive of restricted rotation about the
N‐Ar bond
• The data that has been obtained thus far is• The data that has been obtained thus far is presented for the ortho‐ and meta‐ derivatives with various X and Y groupswith various X and Y groups.
Rotation Energy Barriers of Ortho‐ and Meta‐b i d i idi ( d )
25.0Substituted Anisidine (X = OCH3 and Y = OH)
Ortho‐
Meta‐
1 0
20.0
/mol)
10 0
15.0
ve E (kcal/
5.0
10.0
Relati
0.0‐300 ‐200 ‐100 0 100 200 300
Dihedral Angle (°C)
Fluorine Derivatives
HO
O
HC H3
OHH
OC H3F
F
H
H
NH
H O H
CH3NCH3 H
HH
HH H
H H
O HO H
HH
H HH
F‐meta‐ derivative F‐ ortho‐ derivative F meta derivative
Structures as viewed on MacMolPlt
Rotation Energy Barrier of Ortho‐ and Meta‐Fluorine Derivatives (X = F and Y = OH)
25.0Fluorine Derivatives (X = F and Y = OH)
F‐meta‐
F‐ ortho‐
15 0
20.0
kcal/m
ol) Hydrogen
10.0
15.0
Ene
rgy (k
5.0Relative
0.0‐200 ‐150 ‐100 ‐50 0 50200 150 100 50 0 50
Dihedral Angle (°C)
Chlorine Derivatives
HO
O
HC H3
OHH
OC H3Cl
Cl
H
H
NH
CH3
O
NCH3
O
H
HH
H
H H
O HO H
HH
H HH
Cl‐meta‐ derivative Cl‐ ortho‐ derivative
Structures as viewed on MacMolPlt
Rotation Energy Barrier of Ortho‐ and Meta‐Chlorine Derivatives (X Cl and Y OH)
25.0
Chlorine Derivatives (X = Cl and Y = OH)
Cl‐ ortho‐
Cl‐meta‐
15 0
20.0
kcal/m
ol) Cl meta
Hydrogens
10.0
15.0
y Ba
rrier (k
5.0Energy
0.0‐200 ‐150 ‐100 ‐50 0
Dihedral Angle (°C)
ConclusionsConclusions• The computational data for the meta‐ and ortho‐
derivatives of anisidine, where X=OCH3 and Y=OH,derivatives of anisidine, where X OCH3 and Y OH, indicates a larger energy barrier to rotation (~13 kcal/mol) for the ortho‐ anisidine derivative. Th l b i t t ti i th th• The larger energy barrier to rotation in the ortho‐derivative is supportive of restricted rotation about the N‐Ar bond.
• The energy barrier to rotation for both the ortho‐ and meta‐ derivatives where a halogen (either F, Cl, Br, and I) is being placed at position X and a H atom at position Yis being placed at position X and a H atom at position Y are still being determined.
• Currently there are not enough data points on the rotational energy barrier graphs to make conclusions.
Future WorkFuture Work• The structures of both the ortho‐ and meta‐ derivatives
h h l ( i h F Cl B d I) i b i l dwhere a halogen (either F, Cl, Br, and I) is being placed at position X and a H atom at position Y will continue to be optimized while varying the C‐N‐C‐C dihedral angle atoptimized while varying the C N C C dihedral angle at fixed intervals until complete rotation has occurred.
• Subsequent calculations will be preformed using a larger basis set.
• The structures are being synthesized and 1H NMR of the d i ti b i ll t d t i t tderivatives are being collected at various temperatures.
AcknowledgementsAcknowledgements
• UW‐River Falls College of Arts and SciencesUW River Falls College of Arts and Sciences
• UWRF Chemistry Department
id d d C i l• Midwest Undergraduate Computational Chemistry Consortium
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