Scissoring motion

Fig. 5.3. The three vibrational modes of H2S. (A) Represents the scissoring motion, (B) is the symmetrical stretch and (C) is the asymmetrical stretch.

If a bond has no dipole moment, then Ihe infrared radiation does not cause it to vibrate and no energy is absorbed. However, energy can also be absorbed due to other types of stretcliing and scissoring motions of the molecules in a compound. 

In the O-like state the extracellular ends of helices A, B, C, and D are tilted outward, but their cytoplasmic ends are not displaced. Helix E is tilted also, but around a pivot point near its middle, so its extracellular and cytoplasmic ends are displaced outward and inward, respectively. If this structure is indeed like that of the O state, the implication is that the protein undergoes a scissoring motion in the second half of the photocycle. It begins with a splaying of the cytoplasmic side of the seven helical bundle in M, which continues in N but reverses in O and opens the extracellular cavity instead. These suggested large-scale global motions are in sharp contrast with the relatively small (1-2 A) and more local atomic displacements in the first half of the photocycle. The rationale must be that the structure of the protein in the unilluminated state predisposes it to the early reactions in the cycle, but the later reactions require drastically different conformations. 

Symbols vs, very strong s, strong m, medium w, weak sh, shoulder b, broad v, stretch / , in-plane bend 7, out-of-plane bend 5, scissors motion (CH), aromatic C—H vibrations (CC), aromatic C—C stretch (CCC), aromatic C—C—C bend (C=0), carbonyl stretch or bend (CN), aromatic C—N vibration (A1—OH), hydrated alumina stretch or bend sym, symmetric stretch asym, antisymmetric stretch. 

The amide II band of primary amides comes mainly from the scissoring motion ofNH2. The band is located at 1650-1620cm in solids, and at 1620-1585cm" in dilute solutions (Randall et al., 1949 Clarke et al, 1949 Richards and Thompson, 1947 Jones and Cleverley, 1956). The band is weaker in most cases than the amide 1 band. Tertiary amides have no band in the 1620 cm region since they have no NH2 group. 

Bond angle distortion (angle strain, Baeyer strain), related to the radial scissoring motion of the bond angle... 

So far, we constructed molecules and reasoned their 3D structures in such a fashion that some of you may get the impression that these objects are motionless. The fact is that molecules are very much restless and perform many motions all at the same time. Scheme 9.10 shows the motions that a small molecule like water performs all at once. The molecule vibrates in three modes (Scheme 9.10a) one is a symmetric stretch where the two bonds stretch and shrink in the same direction, and the other is an antisymmetric stretch wherein one bond stretches while the other is shrinking, and finally the two O—H bonds perform a scissoring motion, closing and opening the HOH angle. Additionally, the molecule as a whole also performs rotations around three different axes. 

Noda et al. [17] have measured the in-phase and quadrature spectra of thin films of polystyrene supported on a Teflon film, concentrating on the spectral regions 1425-1525 cm and 2800-3200cm . The former contains two peaks of particular interest, at 1450 and 1490cm. The first of these is made up of overlapping bands from two uncoupled vibrations a CHj scissoring motion in... 

Figure 21-3 (P) Inirared spectrum of cyclohexanamine. Tlie molecule exhibits two strong peaks between 3250 and 3500 cm characteristic of the N-H stretching absorptions of the primary amine functionai group. The broad band near 1600 cm results from scissoring motions of the N-H bonds.

Structural change without bond breaking occurs with a scissoring motion leading to an increase in crystallographic cell volume of ethanol and methanol templated phases E and M of Ni2(bpy)3.(N03)4 during adsorption of the templates. Hysteretic adsorption was observed... 

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