Rate Processes and Nuclear Magnetic Resonance Spectra. II. Hindered Internal Rotation of Amides

Mathematical methods are presented for calculating rate constants of processes which narrow nuclear magnetic resonance absorption lines having discrete components. High resolution proton spectra show that the R1CO‐NR2R3 skeletons of N,N‐dimethylformamide (DMF) and N,N‐dimethylacetamide (DMA) are planar and suggest that N‐methylformamide, N‐methylacetamide, N‐methylformanilide and N‐methylacetanilide exist predominantly in one configuration. The presence of a significant amount of double bond character in the C–N amide bond is proved by the temperature dependent coalescence observed for the chemically shifted proton doublet of the N(CH3)2 groups in DMF and DMA, which gives values of about 22 and 19 kcal respectively for the free energy of activation required for reorientations about the bond.

[1]  E. Purcell,et al.  Relaxation Effects in Nuclear Magnetic Resonance Absorption , 1948 .

[2]  B. Rabinovitch,et al.  Kinetics of the Thermal Cis‐Trans Isomerization of Dideuteroethylene , 1955 .

[3]  W. D. Phillips.  Restricted Rotation in Amides as Evidenced by Nuclear Magnetic Resonance , 1955 .

[4]  I. Amdur,et al.  Structure of Molecules and Internal Rotation , 1955 .

[5]  J. Shoolery,et al.  EFFECTS OF PERTURBING RADIOFREQUENCY FIELDS ON NUCLEAR SPIN COUPLING , 1955 .

[6]  R. A. Ogg.  Study of ultrarapid reactions by nuclear magnetic resonance spectra , 1954 .

[7]  H. S. Gutowsky,et al.  Nuclear Magnetic Resonance Multiplets in Liquids , 1953 .

[8]  H. S. Gutowsky,et al.  Electron Distribution in Molecules. III. The Proton Magnetic Spectra of Simple Organic Groups1 , 1953 .

[9]  P. W. Anderson,et al.  A Mathematical Model for the Narrowing of Spectral Lines by Exchange or Motion , 1954 .

[10]  H. S. Gutowsky,et al.  Apparatus for Nuclear Magnetic Resonance , 1953 .

[11]  Ryogo Kubo,et al.  Note on the Stochastic Theory of Resonance Absorption , 1954 .

[12]  R. A. Ogg.  Proton Magnetic Resonance Spectrum of Ammonia and the Interactions Involved in Hydrogen Bond Association , 1954 .

[13]  E. R. Andrew,et al.  Nuclear Magnetic Resonance , 1955 .

[14]  R. Kurland.  Microwave Spectrum and Planarity of Formamide , 1955 .

[15]  E. R. Andrew,et al.  A proton magnetic resonance investigation of the structure of urea , 1955 .

[16]  H. S. Gutowsky,et al.  Dissociation, Chemical Exchange, and the Proton Magnetic Resonance in Some Aqueous Electrolytes , 1953 .

[17]  F. Bloch,et al.  Line-Narrowing by Macroscopic Motion , 1954 .