Singlet Energy Transfer as the Main Pathway in the Sensitization of Near‐Infrared Nd3+ Luminescence by Dansyl and Lissamine Dyes

In general, sensitization of lanthanide(III ) ions by organic sensitizers is regarded to take place via the triplet state of the sensitizers. Herein, we show that in dansyl‐ and lissamine‐functionalized Nd³⁺ complexes energy transfer occurs from the singlet state of the sensitizers to the Nd³⁺ center. No sensitized emission was observed in the corresponding complexes with Er³⁺, Yb³⁺, and Gd³⁺ ions. Furthermore, the fluorescence of the sensitizers was quenched only in the Nd³⁺ complex and not in the complexes with the other ions. Only Nd³⁺ centers can accept energy from the singlet state of the dyes, because the excited states of Nd³⁺ have a high spectral overlap with the fluorescence of the dansyl and lissamine sensitizers, and because the selection rules allow a fast energy transfer, which apparently is competitive with the fluorescence.     

β-Thiopeptides: Synthesis,NMR Solution Structure,CD Spectra,and Photochemistry

To test the effect of NH−C=S groups (Scheme 1) on the stability of β-peptide secondary structures, we have synthesized three β-thiohexapeptide analogues of H-(β-HVal-β-HAla-β-HLeu)₂-OH ( 1 ) with one, two, and three C=S groups in the N-terminal positions (cf. 2 – 4 and model in Fig. 1). The first C=S group was introduced selectively by treatment with Lawesson reagent of Boc-β-dipeptide esters ( 6 and 8 ). A series of fragment-coupling steps (with reagents as for the corresponding sulfur-free building blocks) and another thionation reaction led to the title compounds with a C=S group in residues 1, 1, and 3, as well as 1, 2, and 3 of the β-hexapeptide (Schemes 2 and 3). The sulfur derivatives, especially those with three C=S groups, were much more soluble in organic media than the sulfur-free analogues (>1000-fold in CHCl₃; Table 1). The UV and CD spectra (in CHCl₃, MeOH, and H₂O) of the new compounds were recorded and compared with those of the parent β-hexapeptide 1 (Figs. 2 – 4); they indicate the presence of more than one secondary structure under the various conditions. Most striking is a pronounced exciton splitting (Δλ ca. 20 nm, amplitude up to +121000) of the ππ*_C=S band near 270 nm with the β-trithiohexapeptide (with and without terminal protecting groups), and strong, so-called `primary solvent effects', in the CD spectra. The CD spectrum of the β-dithiohexapeptide 3 undergoes drastic changes upon irradiation with 266-nm laser light of a MeOH solution (Fig. 5). The NMR structure in CD₃OH of the unprotected β-trithiohexapeptide 4 was determined to be an (M)-3₁₄-helix (Fig. 7), very similar to that of the non-thionated analogue (cf. 1 ). NMR and mass spectra of the β-hexapeptides with C=S and with C=O groups are compared (Figs. 6 and 8).     

Free‐volume variation in polyethylenes of different crystallinities: Positron lifetime,density, and X‐ray studies

High‐quality positron lifetime measurements (70 million total counts) are reported for polyethylenes (PEs) of different crystallinities (X_c = 3–82%). The specific volumes of the crystalline and amorphous phases (V_c and V_a, respectively) were estimated from density and wide‐angle X‐ray scattering (WAXS) experiments. Some samples (those with low values of X_c) were branched PEs, and those with high values of X_c were linear PEs for which X_c was varied with changes in the crystallization temperature. Both V_c and V_a increase with decreasing X_c in the range 0% ≤ X_c ≤ 56% (the branched PEs) but are constant for X_c ≥ 56% (the linear PEs). The lifetime spectra were analyzed with the MELT and LIFSPECFIT routines. Artifacts that can appear in the spectrum analysis were checked via an analysis of computer‐generated spectra. Four lifetime components appeared in all of the PEs; the two long‐lived ones are attributed to pick‐off annihilation of ortho‐positronium (o‐Ps) in crystalline regions (τ₃) and in holes of the amorphous phase (τ₄). With increasing X_c, τ₃ decreases from about 1.2 to 1 ns, τ₄ decreases from 3.0 to 2.5 ns, and the intensity I₄ decreases from 29 to 0%. An increase in I₃ from 6 to 12% was observed. A comparison with simulations shows that the true I₃ value approaches 0 for X_c → 0%. The decrease in I₄ is weaker than the increase in X_c; this leads to the conclusion that the apparent specific o‐Ps yield in the amorphous phase I₄^Xc increases with X_c. Possible reasons for this surprising results are discussed. The fractional free hole volume [h = (V_a ? V_occ)/V_a, where V_occ is the crystalline occupied volume] was estimated from density and WAXS results. Between X_c = 0 and 56%, h decreases from 0.151 to 0.090, but it does not change further above X_c = 56%. The mean size (v) of the local free volumes (holes) estimated from τ₄ decreases from 200 to 150 ų. The number density of holes (N_h) calculated from these values (N_h = h/v) also decreases from 0.8 to 0.6 nm^?3 in the range 0% ≤ X_c ≤ 56%. The values of V_a, V_c, h, and N_h increase with an increasing degree of branching but do not vary for linear PEs. The possible influence of a crystalline–amorphous interfacial phase (three‐phase model) on the observed lifetime parameters is also discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 65–81, 2002     

Pulsed NMR observation of ultradrawn polypropylene

Proton spin-spin relaxation times have been measured as a function of temperature for ultradrawn polypropylene with draw ratios λ up to 24. The three relaxation times T_2a (the longest), T_2i (intermediate), and T_2c (the shortest), observed for all the samples, have been ascribed to the relaxations of the amorphous, constrained amorphous, and crystalline components, respectively. T_2i and T_2a, which reflect the changes in structure and mobility in the noncrystalline regions, decrease with increasing λ; T_2i becomes saturated at λ > 9, whereas T_2a shows a substantial decrease up to λ = 24. The continued decrease in T_2a indicates that the constraint on the amorphous segments keeps increasing up to the highest λ. The associated mass fractions F_a, F_i, and F_c also change with λ. At λ < 9, the increasc in F_i with increasing λ is accompanied by a decrease in F_a, with F_c remaining unchanged. At higher λ, however, F_a is almost constant, and stepwise rises in F_c at about λ = 12 and 24 are accompanied by corresponding drops in F_i. It seems that, in this high draw ratio range, some of the taut molecules are fully extended and are in sufficiently good lateral register to transform into crystalline bridges. This conjecture is supported by the similarity in the λ dependence of F_c and the mass-fraction crystallinity obtained from the heat of fusion.     

Flow of polymer chains and segregation in a flow field with a hybrid simulation

Effects of a flow field (E) on segregation and flow of polymer chains are studied in two dimensions using a hybrid (discrete‐to‐continuum) simulation. The flow rate (j) of polymer chains is found to increase monotonically with E, a linear response in the low field regime followed by a slow approach to saturation in the high field regime. The effective chain permeability (ϕ_c = j/E) varies nonmonotonically on increasing the field E, with a maximum (ϕ_cm) at a characteristic value of the field (in the range 0.2 < E < 2); ϕ_cm depends on the chain length. Chain aggregates exhibit an anisotropic mass distribution due to the field with a molecular bridging at high fields. The longitudinal component of the radius of gyration (R_gx) exhibits a crossover from a random walk (RW) (R_gx ˜ L_c^1/2) at E = 0 to an elongated conformation (R_gx ˜L_c) at E ⪈ 0.2; the transverse component changes from R_gy ˜ L_c^1/2 to R_gy ˜ L_c^1/3. The width of the radial distribution function (ρ(r)) of the monomers increases while its peak varies nonmonotonically with E and is consistent with the observation of anisotropic mass distribution.     

Synthesis and reactions of cysteine‐based telechelic polymers

The radical polyaddition of N‐4‐vinylbenzoyl‐L ‐cysteine methyl ester (VCM) was carried out in the presence of 2,2′‐azobisisobutyronitrile (AIBN, 3 mol %) as an initiator in dimethyl formamide (DMF) with monomer concentrations of 0.5 and 1.0 M at 60 °C for 20 h under nitrogen atmosphere to afford the corresponding polymers [poly(VCM), PVCM] with number‐average molecular weights (M_n)'s of 5300 and 18,000 in 92 and 95% yields, respectively. The obtained polymers had a heterotelechelic structure with thiol and olefin end moieties. The radical polymerization of methyl methacrylate and trityl methacrylate was carried out in the presence of PVCM with AIBN (3 mol %) as an initiator in DMF at 60 °C for 20 h to afford the block copolymers with M_n values in the range of 13,000–26,800 in good yields. PVCM [M_n = 18,000; polydispersity (M_w/M_n) = 1.56] was treated with 4 equiv of NaOH aq. (1.0 M) to afford the polymer having carboxyl groups in the side chain with a M_n of 17,300 and M_w/M_n of 1.88 in 95% yield and was also oxidized to polysulfoxide and polysulfone with 4 equiv of H₂O₂ per sulfide unit in CH₂Cl₂ (1.0 M) for 20 h. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 23–31, 2001     

Synthesis and Tuberculostatic Activity of Some 1,1-Bis-methylthio-2-nitro-ethene Derivatives

1,1-bis-methylthio-2-nitro-ethene was used as a substrate to the syntheses of new heterocyclic compounds. In the reactions, with 1-phenylpiperazine—the corresponding diaminonitroethane 1 , 1,3-diaminonitropropane, and 1,3-diaminonitropropanol—the nitromethylenotetrahydropyrimidine derivatives 2 and 3 were prepared, whereas, with o-phenylenediamine—2-nitromethyleno-benzimidazole 4 were obtained. In the condensation reactions of compounds 2 , 3 , and 4 with benzoyl isothiocyanate, the products 5 , 6 , and 7 were obtained, and afterwards two of them, 5 and 6 , were transformed into the isothiazolines 8 and 9 .

1,1-bis-(4-phenylpiperazino)-2-nitroethane ( 1 ) was exposed to the action of phenyl isothiocyanate and the derivative obtained ( 10 ) was transformed, in the reaction with phenacylbromide, in to benzoylonitrothiophene 11 . The diazo compounds 12 , 13 , and 14 were obtained in the reactions of nitromethylenotetrahydropyrimidines 2 and 3 and of 2-nitromethylenobenzimidazole 4 with benzenediazonium chloride. The derivatives obtained were tested in vitro for their tuberculostatic activity. The compounds 7 (MIC 8–32 μg/mL) and 14 (MIC 16–63 μg/mL) appeared to be the most active compounds.     

Synthesis of [m.n]Cyclophanes: Regiochemistry Transfer from Vinyl Halides to Cyclophanes via Fischer Carbene Complexes

The double benzannulation of bis‐carbene complexes of chromium with α,ω‐diynes generates [m.n]cyclophanes in which all three rings are generated in a single reaction. This triple annulation process is very flexible allowing for the construction of symmetrical [n.n]cyclophanes and unsymmetrical [m.n]cyclophanes as well as isomers in which the two benzene rings are both meta bridged or both para bridged, and isomers that contain both meta and para bridges. The connectivity patterns of the bridges in the cyclophanes can be controlled by regioselectivity transfer from the bis‐vinyl carbene complexes in which the substitution pattern of the vinyl groups in the carbene complexes dictate the connectivity pattern in the [m.n]cyclophanes. This synthesis of [n.n]cyclophanes is quite flexible with regard to ring size and can be used with tether lengths ranging from n=2 to n=16 and thus to ring sizes with up to 40 member rings. The only limitation to regioselectivity transfer from the carbene complexes to the [m.n]cyclophanes was found in the synthesis of para,para‐cyclophanes with four carbon tethers for which the loss of fidelity occurred with the unexpected formation of meta,para‐cyclophanes.     

Reaction of an ammonium eneselenolate derived from a selenothioacetic acid S-ester with electron-deficient alkenes and alkynes

Ammonium eneselenolate 2 derived from selenothioic acid S-ester 1 was reacted with electron-deficient alkenes 4 and alkynes 9 . Ammonium eneselenolate 2 underwent Michael addition with 4 to give two types of Michael adducts, 5 and 6 . Products 6 incorporated two molecules of 4 . In contrast, the reaction of 2 with 9 took place at the selenium atom to give γ-oxo divinyl selenides 10 with high Z-stereoselectivity. During the further elaboration of the reactivity of the products derived from 2 and carbonyl compounds, unexpected reaction was found in the addition of vinylmagnesium bromide to Se-vinyl ester 3 . The spectroscopic data supported the formation of the enol form 12 of β-oxo selenothioic acid S-ester 13 . © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:187–192, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20003     

Light-induced cis/trans isomerization of cis-[Pd(L-S,O)2] and cis-[Pt(L-S,O)2] complexes of chelating N,N-dialkyl-N′-acylthioureas: key to the formation and isolation of trans isomers

Irradiation cis-[M(Lⁿ-S,O)₂] complexes (M = Pt^II, Pd^II) derived from N,N-dialkyl-N′-benzoylthioureas (HLⁿ) with various sources of intense visible polychromatic or monochromatic light with λ < 500 nm leads to light-induced cis?→?trans isomerization in organic solvents. In all cases, white light derived from several sources or monochromatic blue-violet laser 405 nm light, efficiently results in substantial amounts of the trans isomer appearing in solution, as shown by ¹H NMR and/or reversed-phase HPLC separation in dilute solutions at room temperature. The extent and relative rates of cis/trans isomerization induced by in situ laser light (λ = 405 nm) of cis-[Pd(L²-S,O)₂] was directly monitored by ¹H NMR and ¹⁹⁵Pt NMR spectroscopy of selected cis-[Pt(L-S,O)₂] compounds in chloroform-d; both with and without light irradiation allows the δ(¹⁹⁵Pt) chemical shifts cis/trans isomer pairs to be recorded. The cis/trans isomers appear to be in a photo-thermal equilibrium between the thermodynamically favored cis isomer and its trans counterpart. In the dark, the trans isomer reverts back to the cis complex in what is probably a thermal process. The light-induced cis/trans process is the key to preparing and isolating the rare trans complexes which cannot be prepared by conventional synthesis as confirmed by the first example of trans-[Pd(L-S,O)₂] characterized by single-crystal X-ray diffraction, deliberately prepared after photo-induced isomerization in acetonitrile solution.     

Thermoelasticity of networks in swelling equilibrium

A theoretical analysis of the thermoelastic behavior of polymeric networks in swelling equilibrium with excess diluent, using both the kinetic theory of elasticity and the Flory-Huggins theory of mixing, is presented. Our calculations are restricted to the special case of diluents composed of a single constituent. The results are used to obtain the ratio of the energy component of the force f_e to the total force f of rubber networks swollen in excess n-decane, and we find f_e/f to be 0.17, which compares favorably with the value 0.18 reported for the unswollen network. Furthermore, f_e/f is independent of elongation, in accordance with theory. The kinetic theory of elasticity is reasonably well obeyed in this highly swollen system although there remains a small contribution to the force from the C₂ term of the Mooney-Rivlin phenomenological elasticity equation. It is not believed that this has an appreciable effect on f_e/f.     

Gel permeation chromatography: Examination of column efficiency

Gel permeation chromatographic (GPC) separations have been performed with several commercially available column packing materials. The results have been analyzed in the conventional manner to obtain the ratio of weight average to number-average molecular weight, M_w/M_n, for solutes with narrow molecular weight distribution. Various other parameters proposed to measure the efficiency of GPC columns have been evaluated and compared. It is proposed that the experimentally determined value of M_w/M_n for a series of different molecular weight samples with similar, narrow distribution for a given set of columns is a convenient parameter for comparing column efficiency in GPC. This parameter may be calculated from a single chromatogram unlike resolution, R, resolution index, RI, or specific resolution, RS, which require a pair of chromatograms. Results from the M_w/M_n method are usually in agreement with those from the R, RI, and RS calculations but one exception has been found. The number of theoretical plates calculated from the elution of a small molecule or from the polymer peak bears little relation to efficiencies predicted from the proposed M_w/M_n method or from R, RI, or RS.     

Synthesis of Some Pyridothienopyrazolopyrimidopyrimidine and Mercaptomethylpyrazolopyrimidine Derivatives

Mercaptomethylpyrazolopyrimidine (2) was synthesized and reacted with ethyl chloroacetate to afford ethyl pyrazolpyrimidinylmethylmercapto acetate ( 3) , which in turn was converted into the corresponding carbohydrazide 4 . Carbohydrazide 4 reacts with a variety of reagents to give different pyrazolopyrimidines ( 5–12 ). Chloromethyl-pyrazolopyrimidine (1) reacts with chloropyridine to give compound 13 , which was subjected in a series of reactions to give new compounds 14–20 .     

Synthetic Utility of Enaminonitrile Moiety in Heterocyclic Synthesis: Synthesis of Some New Thienopyrimidines

The hitherto unknown 3-amino-5-bromo-4, 6-dimethylthieno [2, 3-b] pyridine-2-carbonitrile ( 4 ) was condensed with p-anisaldehyde affording the Schiff base ( 5 ). Acylation of the thienopyridine derivative ( 4 ) using freshly distilled acetic anhydride gave a mixture of mono and diacetyl derivatives ( 6 ) and ( 7 ). Condensation of ( 4 ) with triethylorthoformate yielded the ethoxymethyleneamino derivative ( 8 ), which was treated with hydrazine hydrate to give the hydrazide derivative ( 9 ), which in turn was converted to a triazolopyrimidine derivative ( 10 ) upon treatment with freshly distilled acetic anhydride. Thiation of ( 4 ) with carbon disulfide afforded the pyrimidine dithione derivative ( 11 ), which was alkylated with ethyl iodide to give the di-s-ethylpyrimidine derivative ( 12 ).On the other hand, treatment of ( 4 ) with formamide yielded the aminopyrimidine derivative ( 13 ), whereas its treatment by formic acid produced the thienopyrimidinone derivative (1 4 ). Chlorination of (1 4 ) with a mixture of phosphorus pentachloride and phosphorus oxychloride gave the chloropyrimidine derivative ( 15 ), which in turn afforded the hydrazide derivative ( 9 ) upon treatment with hydrazine hydrate. Hydrazinolysis of ethyl-3-amino-5-bromo-4,6-dimethylthieno[2,3-b]pyridine-2-carboxylate ( 17 ) gave the hydrazino derivative ( 18 ), which in turn was converted to 8-bromo-7,9-dimethyl-3-formylaminopyrido[3′,2′:4,5]thieno[3,2-d]pyrimidin-4(3H)-one ( 19 ) and 8-bromo-3-diacetylamino-2,7,9-trimethylpyrido[3′,2′:4,5]thieno[3,2-d]pyrimidin-4(3H)-one ( 20 ) upon treatment with formic acid and freshly distilled acetic anhydride, respectively.     

Molecular orbital study of the Q–e scheme in free radical copolymerization

Molecular orbital calculations were used to study free radical polymerization. Calculations show that the monomer is activated during the reaction and the pi bond becomes a diradical. The radical on the carbon that is about to form the new bond is called the e radical in this article. The other is the Q radical. For different monomers it is shown indirectly that changes in the energies of formation of the Q and e radicals are related to changes in the Q and e terms in the empirical Q–e scheme of Alfrey and Price. The polar effect in the Q–e scheme involves the e-radical, unpaired electron density. Specifically, the Q–e sum (e_x + e_y) is correlated with the e radical spin density. Also the e term is correlated with the electron density on the unsubstituted carbon of the monomer. The relationship of the Q radical to the adjacent substituent is shown by correlating ln Q values with the energy of addition of a hydrogen atom to a monomer. These relationships give theoretical meaning to the Q–e terms and allow calculation of Q and e values from molecular orbital properties for small monomers.     

Extraction and sorption studies using linear polymer chains and model networks

Model networks have been prepared by tetrafunctionally endlinking linear polydimethylsiloxane (PDMS) chains having molecular weights M_n in the range 2000–15,000 g mole^?1. The first series of networks were prepared from mixtures containing known amounts of unreactive linear PDMS chains with molecular weights M_d between 1000 and 16,000 g mole^?1. Rates of extraction were used to estimate diffusion coefficients; as expected, they were found to increase with increase in molecular weight M_c = M_n between crosslinks, but to decrease with increase in M_d. The ease with which all of such a diluent could be removed showed the same dependence on M_c and M_d. A second series of networks was prepared from the same reactive PDMS chains without diluents. Sorption and extraction studies using the same diluents were then carried out. The diffusion coefficients for sorption were found to be in the range (1.7–15.0) × 10^?12 m² s^?1 and depended on both M_c and M_d. The amount of diluent absorbed at equilibrium was between 10 and 70%, which is in good agreement with predictions from the Flory equation for dilation in networks, with account of constraints on crosslink fluctuations.     

One‐pot PTC synthesis of polyfused pyrazoles

Thienopyrazole 2 , 3 , 5 , or 6 and thienopyrazolothiazepine 7, 9 , and 11 derivatives were prepared via the reaction of the 3‐aminopyrazoline‐5‐one 1 with CS₂ and different molar ratio of a variety of halo compounds having an active methylene under PTC conditions. Also, treatment of 1 with CS₂ and alcoholic KOH in 2:1:1 molar ratio afforded dipyrazolopyridine derivatives 12 and 14 . On other hand, the pyrazolothiadiazineone derivative 13 was obtained by treating compound 1 with CS₂ and alcoholic KOH in 1:2:2 molar ratio. Under PTC conditions, compound 1 , CS₂, and ethyl cyanoacetate or malononitrile to gave the pyrazolopyridine derivatives 16 and 17 . Coupling of compound 1 with diazonium acetates afforded the hydrazone derivatives 18a,b , which were oxidized with bromine to give pyrazolotriazoles 19a,b or cyclized with aldehydes to give pyrazolotriazine derivatives 20a–e . Bromination of compound 1 afforded monobromopyrazole derivative 21 , which could be condensed to a dipyrazolopyrazindione 23 . Finally, the dibromopyrazole derivative 22 was cyclized with 2‐mercaptoethanol or o‐phenylenediamine to give the spiropyrazoles 24a,b . © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:211–217, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10129     

Modulation of photoswitching profiles by 10,11-dialkoxymethyl substituents in c(2)-symmetric dibenzosuberane-based helicenes

A series of C₂‐symmetric, 10,11‐disubstituted dibenzosuberane (DBS)‐based helicenes 6 a – c with a common 7‐bromo‐α‐tetralin‐based bottom fragment were synthesized. Their absolute stereochemistry was determined to be 10R,11R,P after reductive desulfurization of the corresponding (10R,11R,1′S)‐episulfides with complete stereospecificity. Photoisomerization of the diastereomerically pure (P)‐ 6 c in hexane led to virtually exclusive formation of the opposite M‐form diastereomer (P/M′, <1:>99) at 290 nm. The preferential return of (M′)‐ 6 c to (P)‐ 6 c was also achieved with high selectivity (P/M′, 90:10) at 330 nm. Molecular simulations of (P)‐ 6 c and (M′)‐ 6 c with both DBS conformations suggest that the selectivities of photoswitching are controlled by the conformation of the top DBS template as evidenced by their ¹H NMR spectra. Doping 6 c into a nematic liquid crystal (E7) led to a cholesteric mesophase with modulated pitches, reversible helical senses, and with a switch memory of ternary logic.     

Effect of surfactant adsorption time on the observation of Newton black film in foam film

Observation of Newton black film (NBF) in foam film is possible only with a certain probability W which depends on the concentration C of surfactant in the solution and on the time t_a during which adsorption of surfactant at the solution/air interface has taken place. In the paper, the W(C,t_a) dependence is derived and used to analyze the effect of t_a on the critical surfactant concentration C_c below which NBF in foam film practically cannot be observed. An expression for the C_c(t_a) function is obtained which reveals that C_c decreases substantially with increasing t_a. This expression is found to describe well experimental C_c(t_a) data for foam films obtained from aqueous solution of the therapeutic surfactant INFASURF.     

Solid-state structures of cis- and trans-1-cyclohexyl-2-phenyl-3-(p-toluyl)aziridines

Solid-state structures have been determined for cis- and trans-1-cyclohexyl-2-phenyl-3-(p-toluyl)aziridines using single-crystal X-ray diffraction techniques. The cis isomer crystallizes in the centrosymmetric monoclinic space group P2₁/c (No. 14), with a = 18.669(3)Å, b = 5.709(1)Å, c = 17.412(2)Å, β = 96.29(1)° and Z = 4; the trans isomer crystallizes in the noncentrosymmetric orthorhombic space group Pna2₁ (No. 33), with a = 17.089(2)Å, b = 18.729(3)Å, c = 5.749(1)Å and Z = 4. Full-matrix least-squares refinement of the structural parameters led to the following final agreement factors: R₁ (unweighted, based on F) = 0.040 and R₂ (weighted, based on F) = 0.054 for the 2592 independent reflections of the cis isomer having 2θ_MoK¯α <55° and I>3σ₁, and R₁ = 0.033 and R₂ = 0.031 for the 1504 independent reflections of the trans isomer having 2θ_MoK¯α <55° and I>3σ₁. The statistically significant differences that exist between the two isomers for two bond lengths and ten bond angles (p < 0.05) appear to be the direct result of the p-toluyl group orientation with respect to the cyclohexyl and phenyl substituents. In the cis isomer it is anti with respect to the N-cyclohexyl group and cis with respect to the phenyl group, whereas in the trans isomer it is syn with respect to the N-cyclohexyl and trans with respect to the phenyl group. Three-ring to carbonyl hyperconjugation is correlated with stereoelectronic interactions in the trans isomer. Bonding, determined by X-ray and nmr studies, is discussed for the three-membered aziridine ring proper; while bonding, determined by X-ray studies, is discussed for substituents of the aziridine ring. These aziridinyl ketone compounds are of importance as potential mammalian DNA alkylating anti-tumor agents in solid-state solid-state systems. To date only a trans isomer has demonstrated this biological activity in tumor-bearing rats.