The triplet state decay (T1(nπ*) → S0) of benzaldehydes in the dilute gas phase

The triplet T₁(nπ^*) decay of benzaldehyde (B) and its isotopomers

and

were investigated in the dilute vapour phase (≤0.5 Torr) at room temperature. Following

excitation the quantum yields of the phosphorescence and photodecomposition, and the rate constants of the phosphorescence and the radiationless T₁ → S_o process were determined. Based on these results and in conjunction with theoretical calculations of T₁ → S_o rates and previous data obtained on propynal, the decay mechanism of benzaldehyde was analyzed. It is shown that the important accepting modes of the non-radiative T₁ → S_a decay are the

wagging and the CO stretching modes. In spite of the close vicinity of the T₂(ππ^*) and the T₁(nπ^*) states, the non-adiabatic coupling (communication between ring and carbonyl vibrations is not sufficient to influence the relaxed T₁(nπ^*) decay significantly.     

Sensitized photochemical reactions of some silyl-1,3-butadienes: Synthesis of 2,2,4-trimethyl-3-methylene-2-silabicyclo [2.1.1]Hexane

The photolysis of 2,4,4-trimethyl-4-sila-3-methylene-l,5-hexadiene

yielded 2,2,4-trimethyl-3-methylene-2-silabicyclo[2.1.1]hexane as the only volatile photoproduct in high yield. However, 2,4,4-trimethyl-4-sila-3-methylene-1,6-heptadiene

was found to be photochemically non-reactive under identical reaction conditions, and the 1-substituted butadienes (VI) and (VIII)

underwent cis-trans isomerism on photolysis.     

Zur komplexchemie von 4-zentren-π-systemen : XII. Glyoxaldiiminkomplexe: 1H-nmr-spektren und long range-kopplungen

Glyoxaldiimines (I) RN=CHCH=NR show in the NMR a downfield shift of glyoxalic protons (H_gly) when complexed to

(II: M = Mo, W), but increasing high field shifts when going to

(III) and

complexes (IV). In the tungsten complexes II H_glyW coupling satellites are resolved (J(WH) ≈4–6 Hz); in the phosphine compounds III, IV long range PH_gly coupling is clearly visible. Mechanisms of spinspin interaction are briefly discussed in connection with the EPR results on monoanionic radicals of II–IV.     

On the Pauling electronegativity scales—I

It is shown that the Pauling electronegativity scale χ is closely related to the electrostatic potential near the physical meaningful boundary between the core and valence regions in an atom, and is well reproduced by the relationship:

where N_ν is the valence electron number and the factor f(n) is empirically given by

n being the periodic number.     

Dynamical LEED study of C2H2 and C2H4 chemisorption on Pt(111): evidence for the ethylidyne group

We propose ethylidyne

as the stable formed from C₂H₂ and C₂H₄ chemisorption on the Pt(111) surface (T ≈ 300–350 K). Consistent evidence to support this proposal is given by LEED intensity analysis and high resolution ELS studies of this species.     

Ruling out harmonic couplings as a possible origin of an anomalous isotope effect on the ν5modes in H bonds

Measurements of the transition probabilities of all the IR bands of adipic acid crystals, polarized in the a, c plane and having frequencies in the range 1000–4000 cm^?1show that the anomalous value P_H/P_D= 2 found for the ratio of the transition probabilities of ν_s bands

and

cannot be due to a harmonic coupling of ν_s vibrations with other vibrations.     

Further evidence for the intramolecular charge-transfer interaction between tropylium ion and remote benzene rings in 9,10-dihydro-9,10-(1,2-tropylio)anthracene tetrafluoroborate and its methyl derivatives

A series of 9,10-dihydro-9,10-(1,2-tropylio)anthracene tetrafluoroborates

has been prepared. The intramolecular charge-transfer interactions in

were confirmed by their UV spectra and pK_R+ values. As a model compound 1,2,3,4-tetrahydro-1,4-(1,2-tropylio)naphthalene tetrafluoroborate ($\text{5}$)_was also examined.     

The preparation of fluxional tetrahydrides, (R  H or Me) and their reactions with CO,ButNC or HBr

The cyclometallated monohydrides

(R  H or Me) react with NaOPrⁱ/PrⁱOH/H₂ to give fluxional tetrahydrides, probably

. These are highly fluxional having magnetically equivalent hydridic hydrogens, even at ---100°C. When treated with HBr,

, gives

and with CO it gives a mixture of complexes which are probably

(2 isomers) and

. When treated with Bu^tNC this tetrahydride undergoes similar reactions but another (major) product is formed which appears to be binuclear and fluxional and is probably of type

, with four bridging hydrogens.     

Preparation and properties of some cyclic germanium 1,4-cyclohexanediolates

Colourless liquids of cyclic compounds of the type:

have been prepared by reactions of dibutylgermanium dichloride with cis-1,4-cyclohexanediol or cis,cis,cis-2,5-di-tert-butyl-l,4-cyclohexanediol, in benzene in the presence of a hydrogen halide acceptor.Under similar conditions germanium tetrachloride gave solid products of the type:

Physical and spectroscopic data (IR, Raman, and MS) are given and discussed.     

Investigation of the 2B2 state of H2O+ using valence-bond techniques

Ab initio valence-bond calculations have been performed on the low-lying states of H₂O⁺, with special attention being focused on the

²B₂ state of the ion. The calculated potential energy surface for the

²B₂ state is in qualitative agreement with several previously published molecular orbital calculations in predicting an equilibrium angle of about 60°. This prediction is, however, inconsistent with the most recent interpretation of the high-resolution photoelectron spectrum of H₂O. Examination of the potential energy surfaces for geometries which have been distorted from C_2v symmetry indicates that the

²B₂ and òA₁ states are strongly coupled by the asymmetric stretching motion of the molecular ion. The presence of such a coupling supports the interpretation of the H₂O photoelectron spectrum which invokes excitation of the asymmetric stretching vibration of the ion.     

Doping-addition of arylsulfenyl chlorides to the tricyclo[4,2,2,02,5]deca-3,7,9-triene system: skeletal rearrangements and serendipitious products

“doping-addition” of 2-NO₂C₆H₄SCl to the tricyclo[4,2,2,0^2,5]deca-3,7,9-triene system

occurs to give unusual products: (i) rearranged caged cyclopropane

and (ii) the stable cross-perchlorate

.     

A direct synthesis of 1,3-bis(bromomagnesio)propane

Careful addition of 1,3-dibromopropane

to magnesium in Et₂O yields 1,3-bis(bromomagnesio)propane

which is purified via “magnesacyclobutane”

. Reactions of

with H₂O, CO₂, HgBr₂ and Me₃SnCl are reported. MgBr₂ catalyses the decomposition of

to allylmagnesium bromide

.     

Electrogeneration of triplet states of intramolecular anthracene-amine systems

In the electron transfer between the cation radicals

of the amine moiety of four intramolecular anthra cene-amine systems and the anion radicals B^XXX of some heterocyclic and carbonyl compounds in acetonitrile/toluene, the triplet state of the anthracene moiety

is formed. As intermediates in this process, intramolecular and intermolecular triplet exciplexcs

or

and

or

are discussed.     

An inverse sum rule for isotopic frequencies

A rule relating to the square of the inverse harmonic frequencies of a set of isotopically substituted molecules is developed. The rule is

where Λⁱ_x. is the square of the Xth harmonic frequency of the ith isotopic species, and σⁱ is a weighting factor for the ith species, taken so that

for all a, where Mⁱ_a is the mass of the ath atom in the ith species. An upper bound for the residue (Res)_i can be evaluated from the frequencies of the ith species alone. If the rule is not satisfied, no harmonic force field is compatible with the set of assigned frequencies. The rule is applied to ethylene. The rule is most sensitive to the assignment of the low frequencies. The rule is shown to apply to the vibrations of crystals, including the lattice modes, and if the sum is taken over K = K' ≠ 0 modes, the residue→ 0.     

Dielectric properties of some nematic liquid crystals for dynamic scattering displays

The dielectric constants of three room-temperature nematic mixtures suited for dynamic scattering displays are reported. The asymmetrically substituted azoxybenzenes involved exist as two isomers. One isomer has a positive dielectric anisotropy (Δ =

- ?_⊥ > 0), the other a negative one.     

Laser flash photolysis of iodine-iodide mixture in hydroxylic solvent. Evidence for the existence of the radical anion I

The laser flash photolysis of iodine-iodide mixtures in alcoholic solvents produces transient species absorbing in the red and near infrared region with maxima at 740 and 590 nm. The 740 nm absorption band has already been attributed to the well known I

ion. In this work the 590 nm absorption band is assigned to the I

radical anion which presumably could be formed by the equilibrium reaction: I

+ I₃^- ? I

. The variations of the intensities of the 590 and 740 nm transient absorption bands as a function of I₃^? concentration, temperature and solvent, support this assignment. The kinetics of formation of I

and I

has been studied in solutions of tertiary butanol. An analysis of the experimental results shows that the I

ion could be formed via a mechanism involving an I

intermediate.     

The composition of the evolved gases from the thermal decomposition of certain metal sulfates

By the use of TG—MS, the thermal dissociation of anhydrous CuSO₄ and Al₂(S0₄)₃ was found to proceed according to the reactions:

followed by the reactions:

No SO₃ was indicated in the dissociation of alunite. The sulfate ion appears to dissociate by at least two different mechanisms although the parameter which controls the mechanisms has not been elucidated.     

Some chlorine fluorosulfonate and peroxydisulfuryl-difluoride reactions

Chlorine fluorosulfonate adds exceptionally easy not only to various alkenes, perfluorobenzene, but to alkynes too

The addition of peroxydisulfuryldifluoride to alkyl- and perfluoroalkyliodides leads to unstable adducts, which decompose with the formation of alkylfluorosulfonates and iodine fluorosulfonate; the latter was trapped with fluoroalkenes

The use of ClOSO₂F allows to substitute selectively for the fluorosulfonate group the chlorine atom in monochloroacetic acid esters as well as the fluorine atom in hexafluoroacetone N-fluoroimine

ClOSO₂F serves as an exceptionally active chlorinating reagent for fluorinated alcohols, nitrosocompounds, perfluoroacid amides and particularly for benzene

The reaction of (OSO₂F)₂ with perfluoroacid amides leads to the corresponding N,N-bis(fluorosulfonate)amides, which easily rearrange into alkylfluorosulfonates

The hypochlorites of fluorinated alcohols are stable enough and they, similarly to ClOSO₂F, are able to add to alkenes, fluoroalkenes (but not to perfluoroisobutylene), bis(trifluoromethyl)ketene, trifluoromethylisocyanate and perfluoronitriles

The fluorosulfonatoacetic acid esters are unstable at the ambient temperature, but they can be widely used in situ as a very effective alkylating reagents

     

Synthesis and intramolecular charge-transfer interaction of o-tropyliobiphenyl tetrafluoroborates

A series of o-tropyliobiphenyl tetradfluoroborates

has been synthesized. Evidences are presented to show that

exhibit strong intramolecular charge-transfer interaction between tropylium ion and remote aryl ring. The structure of

was determined by single crystal X-ray diffraction study.