Identification of absolute helical structures of aromatic multilayered oligo(m-phenylurea)s in solution.
The oligomeric aromatic ureas bearing N,N'-dimethylated urea bonds such as 3 have aromatic multilayered structure, based on the (cis,cis)-urea structure, and also have dynamic helical structure (all-R or all-S axis chirality) when the benzene rings are connected at the meta positions. The absolute helical structure of oligo(m-phenylurea)s were identified by the empirical and theoretical studies on the CD and vibrational CD (VCD) spectra. Thus, each enantiomer of the oligo(m-phenylurea)s 4 bearing a chiral N-2-(methoxyethoxyethoxy)propyl group were synthesized. Intense dispersion-type CD spectra of 4 were observed, which indicated the induction of handedness in the helical structure. In the VCD spectra of 4 in the film state, the signals due to the carbonyl and aromatic ring vibrations were seen with negative and positive values for compounds 4a and 4b, respectively. The calculations of both CD and VCD spectra of oligo(m-phenylurea)s 3 without any chiral N-substituent gave the same assignment about the axis chirality of 4. Thus, the absolute configurations of 4a and 4b are all-R and all-S structures, respectively.
Kudo
Mayumi
M
Department of Chemistry, Faculty of Science, Ochanomizu University, 2-1-1 Otsuka, Bunkyo-ku, Tokyo 112-8610, Japan.
Hanashima
Takayuki
T
Muranaka
Atsuya
A
Sato
Hisako
H
Uchiyama
Masanobu
M
Azumaya
Isao
I
Hirano
Tomoya
T
Kagechika
Hiroyuki
H
Tanatani
Aya
A
D002942:Circular Dichroism; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010671:Phenylurea Compounds / Q000737:chemistry*; D012996:Solutions; D021241:Spectrometry, Mass, Electrospray Ionization
D010671:Phenylurea Compounds; D012996:Solutions