1,4-butanediyl

Alkoxyall l All l Peroxides. / /f-Butyl tetrahydropyran-2-yl peroxide [28627 6-5] (1), where R = tert — butyl, X = OR", R = H, R and R" = 1, 4 butanediyl, has been isolated. This is one of many examples of alkoxyalkyl alkyl peroxides which may be prepared by reaction of hydroperoxides with vinyl ethers (139) ... 

Poly 1,2-dioxo-1,4-butanediyl Poly(3-methyl-1 -butene-1,4-diyl)... 

Let us first do a reality check we ll test the ability of some model chemistry methods to perform geometry optimizations on singlet 1,3-propanediyl or trimethylene (CH2-CH2-CH2) and on singlet 1,4-butanediyl or tetramethylene ( CH2CH2CH2CH2 ), simple singlet diradicals. 

Fig. 8.8 The input structures for attempted model chemistry optimizations on 1,4-butanediyl ( CH2CH2CH2CH2 ). All bond lengths and angles in these structures were standard, e.g. C-C ca. 1.5 A, C-H ca. 1.1 A, bond angles ca. 110-120°...

Butanediyl, tetramethylene. Using complete active space (CAS) calculations (below), Doubleday found ten stationary points with tetramethylene-like structures, in work connected with ring-opening of cyclobutane [61]. We saw that model chemistries simply lead to closure or dissociation of input tetramethylene-type structures. 

To do a CASSCF calculation, one must first choose the active space, that is, the relevant MOs. Which MOs are relevant depends on the purpose of the calculation, and on how complete one wants the active space to be. The unattainable limit of course would be full Cl. This will be illustrated with a few examples. Consider the diradicals 1,3-propanediyl and 1,4-butanediyl. Intuitively, it seems that we should consider at least these two MOs the MO that resembles a bonding linear combination (Section 5.2.3.6) of the two p-type atomic orbitals on the end carbons and the... 

Fig. 8.9 The active space for a CASSCF(2,2) calculation on 1,4-butanediyl. There are two relevant MOs the highest occupied and lowest unoccupied MO, and two electrons to be distributed among these. The relevant MOs must be determined by inspection (preferably visual) to be the right ones for the purpose of the calculation see Fig. 8.10...

Fig. 8.10 Visualization of the relevant MOs, 16 and 17, for the active space of a CASSCF(2,2) calculation on 1,4-butanediyl the algorithm will recognize the active space as consisting of the two frontier orbitals (HOMO and LUMO the molecule has 32 electrons) we ensure by visual inspection that these are the two MOs that are localized on the end carbons. If a desired orbital is not a frontier orbital to start with, it can be switched with one (see text). NBO localization was used here. Calculated with the HF/STO-3G basis and localized by the NBO method...

Fig. 8.11 The C2h 1,4-butanediyl diradical relative minimum (no imaginary frequencies), as calculated by CASSCF(2,2)/6-31G (this work) and CASSCF(4,4)/6-31G (Doubleday [61], Fig. 1 and Table III)...

When the latter mixture is treated with the aminium salt at 0°C, the mixture isomerizes completely to the more stable trans,anti,trans isomer. Evidently, the cyclodimerization is reversible at the higher temperature. It is also noteworthy that even the reversal is stereospecific, since none of the other possible diaster-eoisomers are formed. This result is nicely interpreted in terms of the ionization of the trans,syn,trans cyclobutadimer to a long bond cation radical, followed by concerted fragmentation to trans-anethole and the trans-anethole cation radical, avoiding the formation of any cw-anethole. The cyclodimerization of phenyl vinyl ether gives both trans (or anti) and cis (or syn) isomers initially, but subsequent reaction induces some isomerization of the less stable cis isomer to the more stable trans isomer. This is believed to occur through the intervention of a distonic 1,4-butanediyl type cation radical. 

PdP2C3oH32, Palladium, (1,4-butanediyl)-[ 1,2-ethanediylbis(diphenylphos-phine))-, 22 167... 

RhPC32Hn, Rhodium, (1,4-butanediyl)(-q5-pen-tamethylcyclopentadienyl)(tri-phenylphosphine)-, 22 173 Rh2B2N4P4CMIHl2o, Rhodium(I), tetrakis(l-iso-cyanobutane)bis[methylene(di-phenylphosphine)]di-, bis[tetra-phenylborate(l -)], 21 49 Rh20 C,6Hw, Rhodium(l), bis(-q4-1,5-cycloocta-diene)-di-p.-hydroxo-di-, 23 129 IUitO iiHm, Rhodium(l), bis(i)4-l, 5-cydoocta-diene)-di-p.-methoxy-di-, 23 127 RhiOJ K, Rhodium(I), dicarbonylbis-(p-2-methyl-2-propanethiolato)-bis(trimethyl phosphite)di-, 23 124 Rh2Ol2P4S2HM, Rhodium(I), bis(p.-2-methyl-2-propanethiolato)-tetrakis(trimethyl phos-phite)di-, 23 123... 

EINECS 235-935-6 Hexaneperoxoic acid, 2-ethyl-, 1,1,4,4-tetramethyl-1,4-butanediyl ester 1,1,4,4-Tetramethylbutane-1,4-diyl bis(2-ethyiperoxyhexanoate) USP 246 2,5-Dimethyl-2,5-bis(i ethyl-1-hexanoyl-peroxy)hexane 2,5-Dimethyl-2,5-di(2-... 

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