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The membrane-impermeable, nitrene precursor reagent, N-(4-azido-2-nitrophenyl)-2-aminoethyl sulfonate (NAP-taurine), has been employed to study the comparative topology of resealed ghosts and their parent erythrocytes. We have found significant differences in the labeling pattern obtained from resealed ghosts as compared with that obtained from intact erythrocytes. Bands 2.3, 2.4, and 4 (nomenclature adapted from Fairbanks et al. (Fairbanks, G., Steck, T. L., and Wallach, D. F. H. (1971) Biochemistry 10, 2606)) show marked changes in labeling depending on the volume of solution in which the lysis and resealing is carried out. From this result we infer that the positions of certain protein components in the direction normal to the plane of the bilayer is measurably affected by the environment of the membrane.

Thirteen acyl carbamoyl peroxides, a new class of peroxides, were prepared by addition of peroxy-acids to organic isocyanates and their properties were examined. The thermal decompositions, especially of benzoyl N-(p-nitrophenyl) carbamoyl peroxide and benzoyl N-benzoylcarbamoyl peroxide, were studied in crystalline state and in solution, and it was shown that they decompose via three different mechanisms, involving either an amino-radical, a nitrene or a protonated nitrene, depending on reaction conditions.

Thermochemical estimates for aromatic carbenes and nitrenes and their interconversions are reported and allow a unifying explanation of the majority of the experimental data published to date. Chemical activation is a very important, but hitherto ignored factor in these rearrangements. This has given rise to several misinterpretations in the literature, which are now corrected.

The reaction of 4-hydrazino-7-phenylpyrazolo[1,5-a]-1,3,5-triazine (4) with nitrous acid gave 8-phenyltetrazolo[1,5-e]pyrazolo[1,5-a]-1,3,5-triazine (5b), which was determined by pmr and ir spectra to be in equilibrium with 4-azido-7-phenylpyrazolo[1,5-a]-1,3,5-triazine (5a). The equilibrium between the tetrazolo (5b) and azido (5a) forms was studied by pmr and an attempt was made to determine if substituents in the pyrazole nucleus could sufficiently stabilize the tricyclic tetrazolo form (5b) over the bicyclic azido form (5a). Thermal degradation of 5(a ⇌ b) in an aprotic solvent gave 4-amino-7-phenylpyrazolo[1,5-a]-1,3,5-triazine (7), indicating the probability of a nitrene mechanism involved in the decomposition. Heating 5 in aqueous base gave both 7 and the “hydroxy” analog, 7-phenylpyrazolo[1,5-a]-1,3,5-triazin-4(3H)one (6), further substantiating the existence of a nitrene intermediate with a competing nucleophilic displacement of the azido group by a hydroxyl group. Cyclization of 4 with diethoxymethylacetate (DEMA) gave 8-phenyl-s-triazolo[4,3-e]pyrazolo[1,5-a]-1,3,5-triazine (8), which underwent thermal rearrangement to 8-phenyl-s-triazolo[2,3-e]pyrazolo[1,5-a]-1,3,5-triazine (9). Acid catalyzed ring opening of 9 with formic acid gave 3-N-formamido-5-phenyl-2(2-s-triazolyl)pyrazole (10). The failure of 10 to recyclize to 9 with the resultant loss of water, supported the theory that the rearrangement of 8 to 9 might occur simply as a concerted, thermally induced “anhydrous” rearrangement rather than via a covalently hydrated intermediate or a Dimroth type mechanism (in the base catalyzed rearrangement).

Irradiation of 1-azido-2,2,4,4-tetramethylphosphetan 1-oxide (4) in methanol leads by ring expansion to 2-methoxy-3,3,5,5-tetramethyl-1,2-azaphospholidine 2-oxide (17), and by ring opening to methyl (1,1,3-trimethylbut-3-enyl)phosphonamidate (20). The 2,2,3,3-tetramethyl analogue (5) behaved similarly, except that two isomeric ring expansion products (21) and (23) were obtained, in relative yields indicative of the absence of any marked preference for migration of the primary or tertiary ring-carbon atom. In the case of 1-azido-2,2,3,4,4-pentamethylphosphetan 1-oxide [(6), single geometrical isomer], the product (25) of ring expansion was formed as a mixture of geometrical isomers having the methoxy-group cis or trans to the 4-methyl group. The possible involvement of nitrene and metaphosphonimidate intermediates in these reactions is briefly discussed.

Two general methods of conformational analysis by kinetic methods are distinguished, and some definitive experiments are described concerning the validity of the reactivity-model method as employed for cyclohexanes. The fast chemical reaction method is analysed in detail, and potential applications to conformational equilibria of N-alkylpiperidines are discussed. The selectivity of electrophilic addition of some photogenerated carbenes and nitrenes to organic sulphides is examined.

Azido-s-triazines containing –Cl, –OCH3, and –N(CH3)2 groups were synthesized, and their thermal reactions with some hydrocarbons were investigated with respect to the reaction products and the reaction kinetics. With non-olefinic hydrocarbons the reactions were found to proceed via a nitrene inteimediate; in the reactions with cyclohexane, cydohexylamino-s-triazines and amino-s-triazines were obtained. On the other hand, with olefinic hydrocarbons the reactions took place via a. bimolecular mechanism involving a formation of an intermediate of the triazoline type; in the reactions with cyclohexene, cyclohexenylamino-s-triazines were obtained along with amino-s-triazines; In both cases, the yields of alkylamino and alkenylamino-s-triazines increased with the electron-withdrawing power of the substituents in the s-triazine nucleus.

The ring expansion, phenylnitrene (1) azepinylidene (3) has been investigated using the CNDO/2 and Extended Huckel method. Both methods predict that the nitrene-nitrogen of 1 is moving out of the molecular plane on the path of minimum energy. Whether an intermediate 2 is formed or not, the net charge during the reaction indicates that an interaction between the filled nitrene p-orbital and an empty MO of the ring is important in lowering the transition state. The results are compared with experimental results of arylnitrenes and arylcarbenes. The rearrangement of tolylcarbenes to benzocyclobutene and styrene has been reexamined experimentally and interpreted in terms of the dynamics of the out of plane movement of the carbene during ring expansion.

Triethyl phosphite reduction of α-(6- nitroveratrylidene) - γ - butyrolactone ( 6 ) produced a mixture of 3,4 - dihydro - 7,8 - dimethoxy[1.3]oxazino[3.4-a]indol - 1 - one (8), ethyl 5,6 - dimethoxyindole - 2 - carboxylate ( 9 ) and 2,3 - dihydro - 6,7 - dimethoxyfuro[2.3-b]quinoline ( 10 ). Photolysis of the corresponding 6-aminoveratrylidene derivative 11 also produced 10 . Probable mechanisms and spectral evidence for the trans -configuration of 6 and 11 are presented. Nitration of α - veratrylidene - γ - butyrolactone ( 5 ) afforded not only the mononitro compound 6 but also a low yield of α - (α - nitrato - 6 - nitroveratryl) - α - nitro - γ - butyrolactone ( 7 ).

The transients in the flash photolysis of several aromatic azides are identified as triplet nitrenes by their spectra. Their half-lives are determined over a range of concentrations in hexane, ethanol and in several polymeric matrices (polystyrene, sucrose benzoate, polymethylmethacrylate) and are interpreted in terms of three processes : nitrene recombination, hydrogen abstraction from the solvent and reaction of the nitrene with an azido group. Recombination is diffusion-controlled (rate constant ∼109 1. mole–1 sec–1); the same applies to the reaction with an azido group. In contrast, hydrogen abstraction by an aromatic nitrene is a comparatively slow process, corresponding to a life-time (in ethanol) of about 2 × 10–4 sec. This value is corroborated by experiments in soft polystyrene matrices (half-life 10–3sec) and by the rate of intramolecular hydrogen abstraction in the cyclization of 2-nitrenobiphenyl to carbazole (half-life 8 × 10–4 sec). In hard polymeric matrices, hydrogen abstraction is considerably slower (half-lives from 0.1 to 2 sec). Here the rate-determining step is configurational diffusion of CH bonds towards the electron-deficient nitrogen.

Azide-tetrazole tautomerism in tetrazoloazines has been examined by IR, NMR and mass spectrometry. Tetrazolo[1·5-a]pyrimidines (IV) with electron donating groups in position 5 showed no pronounced tendency to tautomerize to azides. An electron withdrawing group (Cl) in position 5, by contrast, favours the azido-form (Ve) which is a metastable solid at room temperature, rearranging to the tetrazole (IVe) at the m.p.; the azide is formed again when the tetrazote melts. In the tetrazolo[1·5-c] pyrimidine/4-azidopyrimidine series (VI-VII) the exactly opposite effect has been observed; electron donating groups in positions 5 and 7 stabilize the azido-form (VII), while in position 8 they favour the tetrazole form. Contrary to general belief, “2,4-diazidopyrimidines” exist in the 5-azido-tetrazolo [1·5-a]pyrimidine form (IVf) with the isomeric 5-azido-tetrazolo[1·5-c]pyrimidine form (VIf) as a likely minor constituent. The diazido-form (Vf) is metastable at room temperature, rearranging to the tetrazoles at the m.p. Liquid SO2 was found to be a suitable solvent for preserving individual tautomers in solution. Tetrazolopyrazine (XI) isomerizes partly to the azido-form (XII) in chloroform and trifluoacetic acid, while tetrazolo[1·5-b]pyridazine (XIII) and tetrazolo[1·5--a]pyridine (I) are completely stable in the tetrazole forms in solution and at 140°. The mass spectra of the labile tetrazoles indicate that the first step in gas-phase pyrolysis is azide-tautomerization with subsequent nitrene formation. Preparation of several tetrazolo-diazines is described.

This review deals with inorganic, organometallic, and organic compounds, as well as with elements, that on the basis of their electronic structure and their reactions can be regarded formally as analogues of carbenes. These “carbene analogues” include in particular the compounds of monovalent boron, aluminum, nitrogen, and phosphorus; those of divalent silicon, germanium, tin, and lead; atomic oxygen; atomic sulfur; and atomic selenium. The preparation and chemical properties of the carbenes and their analogues are compared.

TBAF is a new type of crosslinking agent, which can be used to vulcanize a wide variety of elastomers, both saturated and unsaturated. The reaction involves the first-order decomposition of the azide function to give a nitrene, which in turn reacts with the polymer chain. The vulcanizates are noted for their lack of odor, lack of bloom, excellent physical properties, and excellent heat-aging resistance.

Carbethoxycarbene, carbethoxynitrene, and nitrene generated respectively by the pyrolysis of ethyl diazoacetate, ethyl azidoformate, chloramine and sodium hydroxyl amine-o-sulfonate are shown to irreversibly modify the surface of polyethylene as shown by wettability measurements. The nature of the modification is not fully understood; however, insertion of the carbene or nitrene into a carbon-hydrogen bond appears likely. The modified surfaces thus formed are shown to undergo several classical organic reactions as again determined by wettability measurements.

We report details of an electron paramagnetic resonance study of the triplet ground state of p-nitrophenyl nitrene, oriented in a single crystal of the parent azide. The results are fitted to a spin Hamiltonian of the form H s = D(S z 2 − 1 3 S x 2 ) + E(S x 2 − S y 2 ) + β e H · g · S + S · A · I , 1 with S = 1, I = l and: ∥D∥ = 0.9833 ± 0.0010 cm−1, ∥E∥ = 0.0002 ± 0.0003 cm−1, gxx = 2.0010 ± 0.0006, gyy = 2.0010 ± 0.0006, gzz = 2.0020 ± 0.0008, Axx 0.00172 ± 0.00005 cm−1, Ayy = 0.00055 ±E0.00015 cm−1, Azz = -0.00045 ±0.00015 cm−1. The orientation of the nitrene in the crystal lattice of the azide is determined, and the results interpreted to indicate that the nitrene is slightly twisted from the position occupied by the parent azide. The observed and calculated fine structure transition probabilities are found to be in good agreement. The observed nitrene-nitrogen splittings are analyzed in terms of the transition probabilities and linewidth effects for the hyperfine resonance fields. Evidence of a 14N quadrupolar splitting is observed, but not completely analyzed. The elements of the observed hyperfine interaction tensor are compared with those calculated by the INDO method.

Photolysis of cycloheptene-5-carbonyl azide, endo-norbornene-5-carbonyl azide and o-vinylbenzoyl azide gave very reactive acyl aziridines by internal addition of acyl nitrenes to the olefinic double bonds. Derivatives of 6-azabicyclo-[3,2,2]nonane and 1,2-dihydroisoindol-1-one were prepared. cis-2-Vinyl-cyclopropyl isocyanate, prepared photochemically at −78°, underwent Cope rearrangement at room temperature to 2,3-dihydro-1H-azepin-2-one. The mass spectra of a series of lactams are interpreted.

Dimethyl-N-carbethoxyazepines, isolated from the reaction between ethyl azidoformate and o-, m- and p-xylenes, react with tetracyanoethylene to give [4 + 2] Diels-Alder adducts. Nitroso-benzene is inert toward 2-methylazepines, but reacts with 3,6-dimethyl-N-carbethoxyazepine to give a [6 + 2] cycloadduct. The effect of two methyl substituents on the course of the cycloaddition reactions is discussed.

Irradiation of ethyl azidoformate dissolved in cyclic ethers (IIIA-VA) and acetals (VIA-VIIIA) yields insertion products (IIIB-VIIIB) of carboethoxynitrenes (IIS and IIT). The attack of the nitrenes occurs exclusively at the CH bond adjacent to the ether oxygen or adjoining acetal oxygens to produce a single insertion product in each case. Byproducts are urethane (IX) and the dimerization product (X) of amino radicals (XI). The effects of acetophenone as a sensitizer and of methylene chloride as a diluent have been examined and discussed. Reduction of IIIB and IVB with LAH produces 4-methylaminobutan-1-ol and 5-methylaminopentan-1-ol in 62 and 83% yields, respectively.

Bei der Photolyse wasriger Ir(NH3)5Na -Losungen erfolgt neben einer Stickstoffentwicklung die Bildung eines koordinierten Nitren-Zwischenproduktes als einziges Reaktionsprodukt.

2-Quinolylnitrene (II) rearranges to 1-isoquinolylnitrene (IV) in the gas-phase: the products from either nitrene are o-cyanobenzylcyanide (IX) and 4-cyanoindole (X). 2-Quinoxalylnitrene (XVI) and 4-quinazolynitrene (XIV) likewise give identical products, 1-cyanobenzimidazole (XVIII) and N-cyano-anthranilonitrile (XX), formed by ring contraction and ring opening. Indole ring opens at 900° to give phenylacetonitrile. 9-Nitrenophenanthridine (XXIX) dimerises at 500°, but at 800° ring opens and re-closes to give 4-cyanocarbazole (XXXII) and 9-cyanocarbazole (XXXI). The nitrenes were produced by N2-elimination from the corresponding tetrazoles.

Aus 2-Oximino-1.2.3.4-tetrahydro-chinoxalin (1) entsteht in siedendem Acetanhydrid 2-Acetamino-chinoxalin (6). Diese eigenartige Aromatisierung vollzieht sich aus dem N4. O-Diacetylderivat 2a als Zwischenstufe durch eine synchrone Abspaltung der N4-Acetyl- und der Oxim-Acetoxygruppe als Acetanhydrid. 1 und 3 liefern mit Palladiumkohle in Losung 2-Amino-chinoxalin (7). 3 gibt rein thermolytisch fast quantitativ 7; der Prozes ist der uber Azomethin-nitrene fuhrenden Umwandlung N4-substituierter 1.2.4-Oxadiazolone-(5) in Amidine analog und wurde jetzt erstmals an kondensierten 1.2.4-Oxadiazolen beobachtet. Amidoximes, II Redox Aromatization of 2-Oximino-1.2.3.4-tetrahydroquinoxaline and Its Acyl Derivatives 2-Oximino-1.2.3.4-tetrahydroquinoxaline (1) in boiling acetic anhydride yielded 2-acetaminoquinoxaline (6). This unusual aromatization proceeds via the N4.O-diacetyl derivative 2a by synchronous elimination of the N4-acetyl and acetoxy groups as acetic anhydride. With palladium charcoal in solution both 1 and 3 gave 2-aminoquinoxaline (7). 7 was also obtained in quantitative yield by thermolysis of 3. The latter reaction parallels the transformation of N4-substituted 1.2.4-oxadiazolin-5-ones via azomethine nitrenes into amidines and is the first example of this process with condensed 1.2.4-oxadiazoles.

Difluorocarbene and heptyl nitrene have been shown to irreversibly modify the surfaces of several metals as established by wettability measurements. The critical surface tension values thus obtained are shown to have a strong dependence upon the atomic radius of the underlying metal substrate. Several possible surface structures are discussed; however, the results suggest bonding between the difluorocarbene (or heptylnitrene) biradical and the metal substrate.

Three substituted carbenes, nitrene, and two substituted nitrenes generated by pyrolysis of the appropriate precursors are shown to irreversibly modify the surface of stainless steel. Critical surface tension values obtained from wettability measurements are used to establish the presence of the various reacted species on the stainless steel surface. The infrared frustrated multiple internal reflection spectrum of the difluorocarbene modified stainless steel surface is used to establish that a sigma-diadsorbed-olefin complex may be formed on the metal surface.

β-Styryl isocyanate (1, R H) and its β-methyl- (1, R CH3) and β-phenyl- (1, R C6H5) derivatives underwent both extensive polymerization and the loss of the elements of carbon monoxide upon irradiation at 254 nm in cyclohexane. The formation of 2,5-diphenylpyrazine (3) and indole 4, (R H) from 1, (R - H) and 2,3-dimethyl-5,6-diphenylpyrazine (6) and 2-methylindole (4, R CH3) from 1, (R CH3) provided diagnostic evidence for styryl nitrene (2a) intermediates. The formation of both phenylacetonitrile (5, R H) and α-phenylpropio-nitrile (5, R CH3) was assigned to an initial rearrangement of the residue, C8H6(R)N: (2), into a ketenimine concerted with the elimination of carbon monoxide from 1. Isomerization then produced a nitrile. β3-(β-phenyl)styryl isocyanate (1, R C6H5) gave no product requiring the intermediacy of a nitrene and/or an azirine. The formation of 2,3,4,5-tetraphenylpyrrole (8) was assigned to a dimerization of the isocyanate concerted with or following the elimination of the elements of carbon monoxide and isocyanic acid, and the formation of 3-phenylisocarbo-styril (9) was assigned to a ring-closure of the isocyanate in an excited triplet state. Each isocyanate gave stilbene and trace amounts of oxidative fragmentation into benzaldehyde and benzonitrile. Solvent participation produced benzylcyclohexane and bicyclohexyl. Two unidentified solids, C17H14N2O and C12H14N2O, were obtained from 1, (R CH3).

The photolysis of anthranils (III) led to ring enlargement with the formation of 3-acyl-2-methoxy-3 H -azepines (IV). The reaction in ether containing water or amines yielded the corresponding 2-oxo- or 2-amino-3 H -azepines (V or VII). On the other hand, photolysis of some 7-substituted 3-phenylanthranils (IX and XIII) gave the corresponding 9-acridanone derivatives (X and XIV). A hypothetical scheme (anthranil → nitrene → azirene → azepine) similar to that proposed by Huisgen and Appl for the analogous ring enlargement of phenylazide is applicable to the anthranil rearrangement. By UV and IR spectroscopic methods, the last step was proved to involve a dark reaction of an intermediate (probably azirene species) with protic solvents.

15N-labelling experiments and energy calculations on nitreno-azines and -diazies are in agreement and lead to the theory that both ring contraction and ring expansion in hetarylnitrenes can be one-step processes which are governed mainly by the energy differences between the reacting species and the products.

Both photolytic and pyrolytic fragmentation of the oxadiazolone ring produces carbon dioxide and a residue which may exist in part as an intermediate azomethine nitrene and may react with or without rearrangement and/or further fragmentation. Rearrangement produces carbodiimides 2 and cyanamides 6. Thermal and photo-isornerization of carbodiimides into cyanamides provides a key step in an explanation for the formation of the latter from an oxadiazolone. A highly selective cyclization produces a benzimidazole 3 when a suitable aryl subsliluent is at nitrogen. The formation of N-phenylbenzamidine 7a from 3-phenyl-4-benzyloxadiazolone 5c requires a 1,4-migration from carbon to nitrogen followed by hydrolysis. The same or similar migration of hydrogen and subsequent ring-closure with dehydrogenation provides the formation of 2-phenyl-quinazoline 8. Products which require no rearrangement of the residue include amidines 7 and triazoles 10. A portion of each triazole corresponds to a nitrile, in turn a product along with a simple nitrene;, of more extensive fragmentation of the; oxadiazolone ring. Phenyl, benzyl, and cyclohexyl nitrenes are respectively detected by the isolation of aniline, benzaldehyde and cyclohexanone. Other recombination reactions bring about the formation of triphenyltriazine 13 and triphenylimidazole 14.

Die Polymerisation von Acrylnitril durch eine Reihe von p-substituierten Arylsulfonylaziden wurde in Benzollosung im Temperaturbereich von 100 bis 135°C untersucht. Esergah sich, das die Polymerisationsoeschwindigkeit proportional der Ausgangskonzentration des Acrylnitrils und der Quadratwurzel der Ausgangskonzentration der Arylsulfonylazide war. Es wurde weiter gefunden, das die modifizierte HAMMETTSche Gleichung anwend- bar ist. Die Reaktionskonstante ρ hat den Wert -1,0. Aus den Versuchsergebnissen wurde geschlossen, das die Polymerisation durch das Arylsulfonylimidogen, ein Stickstoff-Radikal, ausgelobst wird. The polymerization of acrylonitrile was carried out in benzene in the temperature range from 100 to 135°C., with p-substituted arylsulfonyl azides as initiators. The rate of polymerization is proportional to the initial concentration of acrylonitrile and to the square root of the initial concentration of the arylsulfonyl azides. Modified HAMMETT'S equation is applicable. The reaction constant ρ has a value of -1.0. It is assumed that the polymerization is initiated by the arylsulfonyl nitrene that is, by nitrogen radical.

N-ニトレンを反応中間体とする反応に関する研究は,この10年間に急速に進歩し, N-ニトレンを生成させる方法としては,すでにいくつかの方法が確立されているが,著者らは, N-ニトレンが関与するものと理解されている諸反応についてもっと深い知見を得るために,適当な化合物を原料として,なるべく余計な試薬を使わないでなるべくおだやかな条件でN-ニトレンを生成させる方法について研究を進めた。この目的のために, 1, 1-ジベンジルヒドラジンおよびそのアニオンと窒化トシルとの反応を詳細に検討し,この反応がN-アジドを経由してN-ニトレンを生成し,既知のN-ニトレンを中間体とする反応を容易に起こすことを確かめた。またN-ニトロソジベンジルアミンおよびN-スルフィニルヒドラジンがベンタカルボニル鉄と反応して容易にN-ニトレンを生成することを明らかにし,これらのN-ニトレンが関与する反応の機構について考察を加えた。 ニトレン窒素が複素芳香環窒素に結合したN-ニトレンを加熱すると,窒素ガスを放出して分解するが,ある種の複素芳香環N-ニレンは窒素の脱離による第一次の分解と同時に,複素環内の室素原子の向う側にある“背骨結合”(backbone bond)が開裂して,もっと小さい断片への分断反応(fragmentation)が起こることがある。この種の分断反応がどんな複素環についてどんな条件のもとに起こるかを検討し,分断反応が起こる原因を,開裂に関与する化学結合の本質に基づいて考察した。

2-Azidoisopthalic acid and 5-azidoisopthalic acid were prepared from the corresponding amines through diazonium salt intermediates. Kinetic studies indicate that they are competitive inhibitors of glutamate dehydrogenase. Photolysis of the enzyme-inhibitor complex with light > 300 nm generates a nitrene which reacts irreversibly with the enzyme and exhibits fluorescence emission at 430 nm when excited by 350 nm radiation.

Pentamethylenetetrazole (VIII) on gas-phase pyrolysis eliminates nitrogen and gives 4-pentenyl-cyanamide (IX). The latter undergoes ring closure to 1-cyano-2-methylpyrrolidine (X). Tetramethylenetetrazole (XII) similarly gives 3-butenylcyanamide (XIII) and 1-cyanopyrrolidine (XIV). Trimethylenetetrazole (XVI) gives nitrogen, ethylene, and a compound C 2 H 2 N 2 , which most likely is N-cyanoformimine, CH 2 NCN.

Seven aromatic azides were photolyzed in organic matrices at 77°K. The primary photoproducts are stabilized and their spectra can be recorded. These primary spectra are assigned to nitrenes; they show the general features associated with open shell aromatic structures, they are independent of the solvent and they disappear when the matrix is softened even at low temperature (90°K). Band assignments for the spectra of the nitrenes and their parent azides are given. The effect of nitrogen on the spectrum of the aromatic radical is discussed in terms of the concepts of Dewar and Longuet-Higgins.