Chair-type

The TCNQ molecule in [TR(bzim)]2-TCNQ is sandwiched between two units of [ J,-N, C -bzimAu]3 in a face-to-face manner so that it is best represented by the formula (7t-[ J,-N, C -bzimAu]3)( j,-TCNQ)(7t-[p-N, C -bzimAu]3). The cyanide groups clearly are not coordinated to the gold atoms. The distance between the centroid of TCNQ to the centroid of the AU3 unit is 3.964 A. The packing of [TR(bzim)]2-TCNQ shows a stacked linear-chain structure with a repeat pattern of-(Au3)(Au3)(p-TCNQ) (Au3)(Au3)(p-TCNQ)- an ABBABB repeat The complex [TR(bzim)]2-TCNQ contains two very short intermolecular Au Au distances of 3.152 A (identical for the two aurophilic bonds). The intermolecular Au Au distance is even shorter than the intramolecular distances in the starting compound, which are 3.475, 3.471, and 3.534 A. The adjacent AU3 units in [TR(bzim)]2-TCNQ form a chair-type structure rather than the face-to-face (nearly eclipsed) pattern reported in Balch s studies of the nitro-9-fluorenones adducts with the trinuclear Au(I) alkyl-substituted carbeniate complexes. 

The stereoselectivity probably results from bidentate chelation of the metal (such as boron) with the oxazolidone carbonyl and the enolate oxygen via a chair-type transition state 9 (Scheme 3-4).la 9... 

A number of substituted propane-l,3-diamine (64) compounds of the type [PtL2] and [PtX2L2] (X = Cl, Br, or NH3) have been described. Several of the latter species exhibited polymorphism which was attributed to either different H-bonded linkages or different chelate ring conformations in the two forms.In solution their n.m.r. spectra are consistent with a preference for a chair-type conformation with the Cl or OH axial.Similar n.m.r. spectral studies have also been reported for some related N-methyl substituted... 

The reaction, which proceeds via a conformationally tight chair-type transition state, is clearly entropically dominated, with a AS of -13 eu. Whereas the known enzyme chorismate mutase from E. coli achieves a 3 x 106-fold accelerated catalysis, the antibody reaches a 104-fold enhancement. A decrease of AS to almost 0 eu points to the presence of an entropy trap. 

In single-wall carbon nanotubes, various chiralities are realized from arm-chair type through zigzag type to chiral type (Figure 2.35), which are known to govern their properties [15]. 

Santhanam R, Noel M. Electrochemical intercalation of cationic and anionic species from a lithium perchlorate-propylene carbonate system—a rocking-chair type of dual-intercalation system. J Power Sources 1998 76 147-152. 

The excellent development of nonaqueous batteries (mostly lithium, metal based and Li ion rocking chair type batteries) created a market for the Li battery grade materials which are manufactured at high purity standards. These materials are manufactured by companies whose expertise lies in the production and distribution of the highly pure solvents and salts. Currently, a great part of... 

When an aldehyde is reacted with a ketone-derived enolate under equilibrating conditions, the thermodynamically more stable 2,3-anti product predominates regardless of the geometry of the enolate. If, however, the reaction is kinetically controlled, the (Z)- and ( )-enolates furnish 2,3-syn and anti aldol products, respectively. This behavior has been interpreted in terms of a chair-type transition state known as the Zimmerman-Traxler model. ... 

The transfer of the allylic moieties from boron to the electrophilic carbonyl carbon proceeds via rearrangement to form intermediate boronic esters C and D (see below). The reaction is highly diastereoselective. The ( )-crotylboronate reacts to give the anfr-homoallylic alcohol and the (Z)-crotylboronate reacts to afford the syn-homoallylic alcohol.This behavior has been interpreted in terms of the Zimmerman-Traxler chair-type transition state model.Because of the double bond geometry, coordination of the (Ei-crotylboronic ester places the Me preferentially equatorial, whereas coordination of the (Z)-crotylboronic ester places the Me axial, as illustrated in the cyclohexane chair-form transition state conformations A and B, respectively. In both cases, the R moiety of the aldehyde must occupy a pseudo-equatorial position to avoid steric repulsion by one of the OR substituents on boron. 

Figure 4. Prediction of stereochemistry of boron enolates 9 and 10 using chair-type six-membered transition state based on the Zimmerman model.

A systematic study of G-rich oligonucleotides containing runs of G residues of various lengths, and with varying numbers intervening residues, revealed a cation-dependent pattern for the G-quadruplex folds adopted by these sequences. It was shown that ions are required to stabilize chair type structures, that is, G-quadruplexes with lateral loops instead of diagonal loops. A minimum of three residues in the central loop and two residues in the two outer loops is required to form an intramolecular chair-type quadruplex, otherwise a mixture of tetramolecular parallel-stranded quadruplexes is... 

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