Neutron diffraction analysis, hydrogen

Nerol, oxidation, 788-9, 790 Neuroprostanes, H2-isoprostane bicycUc endoperoxides, 612 Neutron diffraction analysis, hydrogen peroxide, 96... 

Figure 3. Schematic diagram of the hydrogen-bond structure of p-maltose monohydrate (MALTOS11). The anrows indicate infinite chains. Distances and angles are from the neutron diffraction analysis.

Pepinsky R. Hydrogen-deuterium replacement in neutron diffraction analysis, Eleventh Annual Pittsburgh Diffraction Conference, Program... 

Fig. 30. The results of a neutron diffraction analysis of the Fe[P(OMe)3]3(T)3-C8Hi3) + cation, which provided the first definitive evidence for metal-hydrogen-carbon interaction (Ref. 133)...

A neutron diffraction analysis of H2O and D2O ice Ih at different temperatures has shown that, in addition to the disordered hydrogens, the oxygen atoms are also disordered about sites 6 pm off the hexagonal axis. 

Table 2.4. Hydrogen bond geometry in the a- and / -deutero oxalic acid dideuterates from neutron diffraction analysis [83]...

Table 5.4. Hydrogen-bonding effects on the covalent-bond lengths in formamide, acetamide, fluoroacetamide and thioacetamide. A (A) refers to differences between values from the neutron diffraction analysis (corrected to rest structure) and the theoretical value for the isolated molecule (at rest) at the HF/3 - 210 level...

A very interesting example of three-center hydrogen bonding is provided by the neutron diffraction analysis in 1966 of the para- and ferroelectric crystals of ammonium sulfate [451]. The transition from one to the other state involves a change in hydrogen bonding in which three of the five three-center hydrogen bonds become two-centered (see Thble 8.2). 

These compounds are unique alkylating or arylating reagents and their reactivity has been reviewed [25,26], Some chemoselective reactions are presented. The addition reaction of aldehydes to 10 proceeds faster than that of ketones [23,25,27,28], Compound 8 reacts chemoselectively with an acetal, and not with an ester group [29], The structure of TiMeCl3(dmpe) (12) has been determined both by X-ray and neutron diffraction analysis. The latter confirms that there is a unique agostic interaction of the a-hydrogen atom with the titanium atom [30,31], This weak interaction stabi-... 

P. Vishweshar, N. J. Babu, A. Nangia, S. A. Mason, H. Puschmann, R. Mondal and J. A. K. Howard, Variable temperature neutron diffraction analysis of a very short O-H- O hydrogen... 

T. F. Koetzle (1981). J. Am. Chem. Soc., 103, 1458-1466. An interstitial hydrogen atom in a hexanuclear metal cluster X-ray and neutron diffraction analysis of [(Ph3P)2N]"[HC06(CO),5r... 

This structure was studied independently by Parthasarathy (58) and by a group at Glasgow (59). The disagreement between the structures originally reported has now been resolved (60). A neutron-diffraction analysis, )delding more precise locations for the hydrogen atoms, has also been published (61). The structure is shown in Fig. 12, relevant dimensions in Table 11. 

Examples of very short hydrogen bonds that are not S3mimetrical are of special interest. We have already given one example in Sect. XIX. Another is the cation represented in (26) whose structure (in the hydrated chloride) has been determined by X-ray (99) and subsequently be neutron-diffraction analysis (700). This cation is a hydrogen-chelate, like the hydrogen-maleate anion, and the hydrogen bond is similarly short ... 

Stretching peak is broadened and intensified upon formation of a H bond. NMR spectroscopy can also be used to detect H bonds because formation ofa H bond leads to a downfield chemical shift. X-ray diffraction analysis and neutron diffraction analysis allow us to obtain structural details of H bonds. Determination of the position of the hydrogen atom in small molecules is possible with these methods, although the r(X-H) values determined by X-ray analysis tend to be shorter than the real internuclear distances [lej. However, for larger biomacromolecules such as proteins, the positions of hydrogen atoms are usually not resolved by X-ray diffraction [16]. 

---