Showing papers on "Norbornene published in 2001"
TL;DR: A full literature and patent account (about 100 references) is given on work describing the vinyl polymerization to homo-polynorbornene in this article, where metal catalysts are presented and important polymer product properties are emphasized.
Abstract: A full literature and patent account (about 100 references) is given on work describing the vinyl polymerization to homo-polynorbornene. The interest in vinyl homo-polynorbornene is driven by its dielectric and mechanical properties for the technical application as an interlevel dielectric in microelectronics applications. The norbornene/olefin copolymerization is covered to some extent for comparison. The metal catalysts are presented and important polymer product properties are emphasized.
275 citations
TL;DR: A full literature and patent account (about 100 references) is given on work describing vinyl polymerization of form the homopolymer poly(norbornene) as discussed by the authors, which is driven by its dielectric and mechanical properties for thte technical application as an interlevel dielectrics in microelectronics applications.
Abstract: A full literature and patent account (about 100 references) is given on work describing vinyl polymerization of form the homopolymer poly(norbornene). The interest in vinyl-poly(norbornene) is driven by its dielectric and mechanical properties for thte technical application as an interlevel dielectric in microelectronics applications. For comparison, the norbornene/olefin copolymerization is discussed also. The metal catalysts are introduced and important polymer product properties are emphasized. The six possible isomers for stereoregular poly(norbornene) are presented.
195 citations
TL;DR: Aqueous coordination polymerization of ethylene by different neutral nickel(II) complexes ((X^O)NiR(L)) (X ) P: type 1 ;X ) N: type 2) was investigated in this paper.
Abstract: Aqueous coordination polymerization of ethylene by different neutral nickel(II) complexes ((X^O)NiR(L)) (X ) P: type 1 ;X ) N: type 2) was investigated. With catalyst precursors of type 1, productivities and molecular weights were reduced by comparison to conventional polymerization in organic solvents. This effect results to a large extent from a lowering of the chain growth rate due to a low concentration of ethylene at the catalytically active centers in the aqueous polymerization. The catalysts are stable in water for hours. Stable latices of low-molecular-weight linear polyethylene were obtained with a hydrophilic complex of type 1 in an emulsion-type polymerization (Mw ca. 3 10 3 g mol-1, Mw/Mn 2-3; solids content of polymer dispersions up to 10%). With complexes of type 2, productivities in aqueous ethylene polymerization were also reduced by comparison to polymerization in organic solvents. However, moderately branched semicrystalline polymers of high molecular weight are accessible (Mn > 10 4 g mol -1 ). Employing norbornene as a comonomer, high-molecular-weight amorphous copolymers were obtained in water as a reaction medium. Ethylene solubility in water-acetone mixtures was estimated experimentally.
164 citations
TL;DR: In this paper, the effect of coordinating solvents and the uptake of endo vs exo isomers for functionalized norbornenes was tested and it was shown that the endo isomer reacts more slowly than the exo wasomer and both isomers react much more slowly compared to norbornene derivatives lacking coordinati...
156 citations
TL;DR: In this paper, the synthesis of poly(norbornene)s (PNB)s bearing acetoxy, hydroxy, and vinyl end groups was accomplished using norbornene, ruthenium-based olefin metathesis catalyst (PCy3)2Cl2RuCHPh, and allyl acetate as a chain transfer agent (CTA).
Abstract: The synthesis of a variety of poly(norbornene)s (PNB)s bearing acetoxy, hydroxy, and vinyl end groups was accomplished. PNBs with an acetoxy group at one terminus and a vinyl group at the other were prepared using norbornene, ruthenium-based olefin metathesis catalyst (PCy3)2Cl2RuCHPh, and allyl acetate as a chain transfer agent (CTA). Employing a more active catalyst, (1,3-dimesityl-4,5-dihydroimidazol-2-ylidene)(PCy3)Cl2RuCHPh, and 1,4-diacetoxy-2-butene as the CTA afforded telechelic PNBs bearing acetoxy groups at both ends of the polymer chains. Molecular weights were controlled by varying the initial monomer/CTA ratio and were in agreement with their theoretical values. Using a similar procedure, acetoxy end-terminated PNBs were also obtained by degradation of high molecular weight PNB. Removal of the acetoxy groups afforded the corresponding hydroxy-terminated polymers with number-averaged functionalities close to two. Mechanisms are proposed for the formation of the end-functionalized polymers. Cor...
151 citations
TL;DR: Treatment of a variety of alkenes with boronic acids, boronates, and sodium tetraphenylborate furnishes beta-arylated and alkenylated products in good to excellent yields.
143 citations
TL;DR: In this article, a method for growing uniform, covalently attached polymer onto crystalline Si(111) surfaces was described, where the surface-bound chlorine was replaced by a terminal olefin using a Grignard reaction using a ruthenium ring-opening metathesis polymerization catalyst.
Abstract: We describe a method for growing uniform, covalently attached polymer onto crystalline Si(111) surfaces H-Terminated Si was first chlorinated, and the surface-bound chlorine was then replaced by a terminal olefin using a Grignard reaction A ruthenium ring-opening metathesis polymerization catalyst was then crossed onto the terminal olefin, and the resulting surface was subsequently immersed into a solution of monomer to produce the desired surface-attached polymer The method provides a direct linkage between the polymer and the Si without the presence of an electrically defective oxide layer Growth of the polymeric layer could be controlled by varying the concentration of monomer in solution, and polynorbornene films between 09 and 5500 nm in thickness were produced through the use of 001−244 M solutions of norbornene
142 citations
TL;DR: 1,5-Selectively disubstituted 9,10-diphenyl- or alkylphenylphenanthrenes are obtained by reaction of ortho-substituting aryl iodides and diphenyl/alkyl phenylacetylenes in the presence of palladium and norbornene as catalysts.
135 citations
TL;DR: In this article, E−N copolymers were synthesized with the C2 metallocene rac-Me2Si(2-Me-[e]-benzindenyl)2ZrCl2 (3) and with the constrained geometry Me2Si (Me4Cp)(NtBu)TiCl2(4) in the presence of methylaluminoxane.
Abstract: Ethylene−norbornene (E−N) copolymers were synthesized with the C2 metallocene rac-Me2Si(2-Me-[e]-benzindenyl)2ZrCl2 (3) and with the constrained geometry Me2Si(Me4Cp)(NtBu)TiCl2 (4) in the presence of methylaluminoxane. The E−N copolymerizations were carried out using a variety of monomer feed compositions. Copolymers were fully characterized by 13C NMR spectroscopy, gel permeation chromatography, and differential scanning calorimetry. Copolymer microstructures were analyzed in detail, through a procedure which accounts for the stoichiometric requirements of the copolymer chain as well as for the measured areas of 13C NMR signals. This analysis, which quantifies the differences in sequence distribution and tacticity of the polymers, evidenced that mainly alternating stereoregular and stereoirregular copolymers were prepared with 3 and 4, respectively. The copolymer prepared with 4 contains both meso and racemic NEN sequences and small amounts of meso and racemic NN diads, while the alternating copolymer p...
118 citations
TL;DR: Neutral palladium complexes bearing pyrrole−imine ligands (I−III) have been synthesized, and their use as catalysts for olefin and vinyl monomer (co)polymerizations was investigated as mentioned in this paper.
Abstract: Neutral palladium complexes bearing pyrrole−imine ligands (I−III) have been synthesized, and their use as catalysts for olefin and vinyl monomer (co)polymerizations was investigated. Methyl acrylate (MA) has been homopolymerized in excellent yields (>95%) using these complexes. Copolymerizations of MA with norbornene or 1-hexene in the presence of these catalysts produce acrylate-enriched copolymers. Hypothesizing that metal enolates are potential intermediates in some of these polymerizations, palladium enolate complexes (IV−VII) containing ligand 1 were tested for their catalytic activity. Surprisingly, these complexes proved inactive toward acrylate and/or olefin polymerizations. Further mechanistic studies have shown that the homo- and copolymers obtained using these complexes arise from a radical mechanism rather than the anticipated metal-mediated process.
112 citations
TL;DR: In this article, a ring-opened poly(norbornene) backbone containing ring opened poly(n) derivatives in the side chain has been prepared efficiently by repeating the ring-opening metathesis polymerizations (ROMP) using well-defined molybdenum initiator of the type, Mo(CHCMe2Ph)(N-2,6-iPr2C6H3)(OR)2 [OR = OCMe3, OCMe(CF3)2]2].
Abstract: Various poly(macromonomer)s of ring-opened poly(norbornene) backbone containing ring-opened poly(norbornene) derivatives in the side chain have been prepared efficiently by repeating the ring-opening metathesis polymerizations (ROMP) using well-defined molybdenum initiator of the type, Mo(CHCMe2Ph)(N-2,6-iPr2C6H3)(OR)2 [OR = OCMe3, OCMe(CF3)2]. The key steps for synthesis of the macromonomer are both exclusive end-capping and quantitative esterification of hydroxy group at the polymer chain end with norbornene carboxylic acid chloride, and the use of Mo(CHCMe2Ph)(N-2,6-iPr2C6H3)[OCMe(CF3)2]2 was found to be an effective initiator in order for this polymerization to proceed to the complete conversion. The present synthetic approach should be useful for preparing various poly(macromonomer)s containing functional groups, especially amphiphilic poly(macromonomer) architectures precisely.
TL;DR: A series of homogeneous and heterogeneous palladium(II)-catalysts and their use in Heck-couplings is described in this article, which leads to a significant perturbation of almost perfect square coordination of the corresponding lowereddabilities.
TL;DR: In this article, the polymerization of norbornene with two new families of late transition metal-based catalysts derived from: (i) Ni and Pd complexes bearing bulky diammine ligands, with the general formula [ArN=C(R)-C (R)=NAr]MeX 2 and (ii) Fe and Co complexes with bulky arylimine ligands with a general formula [(2,6-ArN =C(Me)) 2 C 5 H 3 N]MX 2]
Abstract: The polymerization of norbornene with two new families of late transition metal-based catalysts derived from: (i) Ni and Pd complexes bearing bulky diammine ligands, with the general formula [ArN=C(R)-C(R)=NAr]MeX 2 and (ii) Fe and Co complexes bearing bulky arylimine ligands with the general formula [(2,6-ArN=C(Me)) 2 C 5 H 3 N]MX 2 is reported. New Co-based complexes have been tested as well. A prevailingly vinylic, amorphous polymer was obtained with all the catalysts tested, whose solubility in organic solvents is substantially dependent on the molucular weight. Polymerization activity greatly varies from one catalyst to another and depends rather on the metal than on the ligand. Solvent polarity and temperature greatly affect the polymerization yields. Besides a dramatic reduction of molecular weights, the addition of small amounts of 1-hexene produces a noticeable increase in the catalytic activity. NMR analysis shows that in all cases a certain percentage of ROMP polymer is present and that, in general, the variations in polymerization conditions, which produce an increase in activity, simultaneously affect a reduction of the ROMP percentage.
TL;DR: In this article, the host/guest interaction was studied by FT-Raman, thermogravimetric analysis and N2 adsorption, and the results showed that the RCM of diallylamine and diethyldiallylmalonate showed very high activity towards norbornene.
Abstract: Heterogeneous hybrid catalysts with respect to the metathesis of olefins have been prepared by ligand exchange reaction between Ru-alkylidene complexes (Grubbs’ type) and a phosphinated mesoporous matrix (P-MCM-41). The host/guest interaction is studied by FT-Raman, thermogravimetric analysis and N2 adsorption. Catalytic tests in olefin metathesis reveal ROMP activity towards norbornene, even in aquatic environment, and a very high activity for the RCM of diallylamine and diethyldiallylmalonate.
TL;DR: In this paper, the authors investigated the relationship between the composition of ethylene/norbornene copolymers and their thermal properties and showed that there is no linear correlation between the amount of norbornene incorporated in copolymer and thermal behavior.
Abstract: This study involves research on possible relationships between the composition of ethylene/norbornene copolymers and their thermal properties. The copolymers were fully characterised by differential scanning calorimetry (DSC), 13 C NMR spectroscopy, Fourier transformation infra-red (FTIR) and Raman spectroscopy. The results of this study show that there is no linear correlation between the amount of norbornene incorporated in copolymers and thermal behaviour when copolymers containing high norbornene content and different microstructures are considered. The latter of which was found to be extremely sensitive to the catalyst used in its preparation.
TL;DR: Ring-opening metathesis polymerization (ROMP) of norbornene (NBE), catalyzed by water-soluble ruthenium alkylidenes 1, RuCl2(PCy2(C5H10NMe2Cl))2(CHPh), or 2, Rucl2(TPPTS)2 (CHCO2Et) (TPPTS = tris(3-sulfonatophenyl)phosphine, sodium salt), has been carried out in emulsion as mentioned in this paper.
Abstract: Ring-opening metathesis polymerization (ROMP) of norbornene (NBE), catalyzed by water-soluble ruthenium alkylidenes 1, RuCl2(PCy2(C5H10NMe2Cl))2(CHPh), or 2, RuCl2(TPPTS)2(CHCO2Et) (TPPTS = tris(3-sulfonatophenyl)phosphine, sodium salt), has been carried out in emulsion. Polynorbornene latexes (PNBE) can be obtained in high yields, in the absence of floc, and with high solids, if Dowfax is used as surfactant. The nucleation mechanism of the polymerization has been found to be a continuous homogeneous nucleation. The resulting polymer particles are formed of aggregates of small primary particles, stabilized by the highly ionized chain ends. Typical particle sizes are ranging from 50 to 100 nm, even at higher solids. Less strained olefins, such as cyclooctene, COE, and 1,5-cyclooctadiene, COD, cannot be efficiently polymerized by catalysts 1 or 2. Nevertheless, these monomers are polymerized by a hydrophobic catalyst, 3, RuCl2(PCy3)2(CHPh). To form colloidal objects, the catalyst is dispersed into water thr...
TL;DR: Gibson et al. as discussed by the authors showed that the polydispersity indices (PDIs) of the polymers obtained from initiator 1 are generally broad (between 1.3 and 1.5), which arises from an unfavorable rate of initiation relative to propagation (k_p) as well as considerable secondary metathesis (backbiting), which creates difficulties when attempting to accurately predict polymer molecular weight a priori or when preparing well defined block copolymers (where complete initiation is necessary).
Abstract: Ring-opening metathesis polymerization (ROMP) has evolved into a valuable tool for the polymer chemist. The polymerization is generally mild and well controlled, and a large pool of readily available cyclic olefins (monomers) can be polymerized to nearly any size or shape. Employing the Ru-based initiator 1 (or its more active derivative 2) permits incorporation of high degrees of functionality and affords polymers with novel mechanical, electronic, and more recently biological properties. However, the polydispersity indices (PDIs) of the polymers obtained from initiator 1 are generally broad (between 1.3 and 1.5), which arises from an unfavorable rate of initiation (k_i) relative to propagation (k_p) as well as considerable secondary metathesis (“backbiting”). This creates difficulties when attempting to accurately predict polymer molecular weight a priori or when preparing well-defined block copolymers (where complete initiation is necessary). A recent disclosure from Gibson and co-workers revealed that the initiation efficiency of 1 was enhanced when the PCy_3 ligands were substituted with Cy_2PCH_2Si(CH_3)_3. When the resulting complex (3) was used to initiate the ROMP of norbornene derivatives (similar to 4), the k_i/k_p was found to be 4.35 (up from 0.06 when initiated with 1), and the resulting polymers were nearly monodispersed (PDIs ∼ 1.1). The enhanced initiation was attributed to a combination of the lower basicity and smaller size of Cy_2PCH_2Si(CH_3)_3 (relative to PCy_3) which respectively helped facilitate phosphine dissociation (a key step in Ru-based ROMP, see below) and increase monomer accessibility.
TL;DR: The synthesis of fused aromatic carbocycles from aryl iodides and difunctional acceptors is outlined, based on a palladium-catalyzed aromatic substitution followed by an intramolecular Heck sequence.
Abstract: The synthesis of fused aromatic carbocycles from aryl iodides and difunctional acceptors is outlined. This methodology is based on a palladium-catalyzed aromatic substitution followed by an intramolecular Heck sequence. Under the optimized conditions (Pd(OAc)2 (10 mol %), tri-2-furylphosphine (20−30 mol %), norbornene (2 equiv), Cs2CO3 (2 equiv), CH3CN, reflux), bromoenoates react with aryl iodides bearing numerous substituents (F, Cl, CF3, Me, etc.). The expanded description of our initial work as well as the use of polysubstituted aryl iodides is described.
TL;DR: In this paper, sterically hindered olefins like norbornene, dimethanooctahydronaphthalene (DMON), 4-methylpentene, and 3-methylbutene can be copolymerised with ethene by metallocene/MAO catalysts.
Abstract: Sterically hindered olefins like norbornene, dimethanooctahydronaphthalene (DMON), 4-methylpentene, and 3-methylbutene can be copolymerised with ethene by metallocene/MAO catalysts. Different C 2 -, C s - and C 1 -symmetric and meso-zirconocenes were used. Only isolated and alternating norbomene sequences but no norbornene blocks are formed by substituted [Me 2 C(Cp-R)(Flu)]ZrCl 2 catalysts. The alternating microstructure leads to melting points up to 270°C for ethene-norbornene copolymers and up to 380°C for the semicrystalline alternating copolymer of ethene and DMON. Other sterically hindered olefins such as 3-methylpentene build more blocky structures with high glass transition temperatures. The mechanism for the insertion reaction of the different catalysts is discussed.
IBM1
TL;DR: In this article, a pendant hexafluoroisopropanol group was used as a building block for 157nm resist polymers, which can be placed in either acrylate or norbornene repeat units.
Abstract: Based on UV measurements at 157nm of in-house fluoropolymers we have selected (alpha) -trifluoromethylacrylate and norbornene bearing a pendant hexafluoroisopropanol group as our building blocks for 157nm resist polymers. Polymers consisting of these repeat units have an optical density/micrometers of 3 or below at 157nm. We have found that the (alpha) -trifluoromethylacrylate derivatives conveniently undergo radical copolymerization with norornenes, which has provided a breakthrough in preparation of our 157nm resist polymers. This approach offers flexibility and versatility because an acidic moiety or acid-labile group can be placed in either acrylate or norbornene repeat unit. Other platforms of interest include all acrylic, all-norbornene, and acrylic-styrenic polymers.
TL;DR: The solid-state structure of the first nickel compound containing a chelating amino−indenyl ligand was resolved and confirmed the chelation of the amine tether to the nickel center as mentioned in this paper.
TL;DR: In this paper, ten copolymers of ethylene and norbornene, synthesized by a metallocene catalyst, covering the composition range from 31 to 62 mol-% of norbornenes, have been studied by stress-strain, microhardness and dynamic mechanical measurements.
Abstract: Ten copolymers of ethylene and norbornene, synthesised by a metallocene catalyst, covering the composition range from 31 to 62 mol-% of norbornene, have been studied by stress-strain, microhardness and dynamic mechanical measurements. These copolymers show a single glass transition and the correlation between T g and the norbornene content is quite good. The inclusion in the polymer chain of rigid norbornene units, with the corresponding increase in T g , leads to considerably higher Young moduli and microhardness values in these cyclo-olefin copolymers. The same result is found for the yield stress: this parameter shows an increase by a factor of two in studied copolymers. Two relaxations, α and γ have been found by means of dynamic mechanical analysis of these copolymers. The results show that the γ relaxation has a similar origin to that of polyethylene and therefore its intensity diminishes as the proportion of ethylene segments in the copolymers decreases. On the contrary, the α relaxation of the copolymers has a completely different origin than that of polyethylene. Thus, this relaxation represents the glass transition in the copolymers, associated with the amorphous character, while it is attributed to motions in the crystalline regions of the parent homopolymer, polyethylene.
TL;DR: In this paper, a range of ethylene/norbornene copolymers were synthesized using the commercially available rac-Et(Ind)2ZrCl2 metallocene catalyst.
Abstract: A range of ethylene/norbornene copolymers were synthesized using the commercially available rac-Et(Ind)2ZrCl2 metallocene catalyst. A large window of norbornene contents, between 30 and 55 mol % was used to facilitate the interpretation of the results. The polymers were characterized by means of wide-angle X-ray scattering, differential scanning calorimetry, and dynamic mechanical thermal analysis. The X-ray diffractograms showed two amorphous halos, the low-angle one increasing in the intensity with norbornene content. Calorimetric and dynamic mechanical results led to a linear relation between the glass transition temperature and the norbornene content. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2159–2165, 2001
TL;DR: In this paper, the structure of complexes 2, 3, and 5 have been established by X-ray diffraction data and Spectroscopic (IR and NMR) data are also given.
TL;DR: In this article, the homo and copolymerisation of norbornene and styrene with nickel bis(acetyl acetonate)/methylaluminoxane system were systematically investigated.
TL;DR: In this article, the PNP palladium(II) complexes [Pd(PNP)(olefin)](BF4)2 [olefin = ethylene, propene, styrene, (Z)-2-butene, (E)-2)-butenes, norbornene; PNP = 2,6-bis(diphenylphosphanylmethyl)pyridine] have been prepared and characterized by 1H, 13C, and 31P NMR spectroscopy.
Abstract: Dicationic olefin palladium(II) complexes [Pd(PNP)(olefin)](BF4)2 [olefin = ethylene, propene, styrene, (Z)-2-butene, (E)-2-butene, norbornene; PNP = 2,6-bis(diphenylphosphanylmethyl)pyridine] have been prepared and characterized by 1H, 13C, and 31P NMR spectroscopy. The coordinated double bond in these complexes is strongly electrophilic, and easily adds a variety of nucleophiles NuH (H2O, MeOH, aliphatic and aromatic amines). This reaction competes with olefin displacement in a rapidly reversible equilibrium process, as a result of which the addition products can also be obtained starting from the substituted compounds [Pd(PNP)(NuH)](BF4)2 and the appropriate olefin. Equilibrium constants for the addition and substitution reactions have been determined in a number of cases. Proton abstraction from [Pd(PNP)(CHRCHR′NuH)]2+ by NaHCO3 quantitatively drives the equilibrium to β-functionalized alkyl complexes of the general formula [Pd(PNP)(CHRCHR′Nu)](BF4), which are unusually stable to β-H elimination.
TL;DR: A convenient procedure for the preparation of enantiopure 10-(R-thio)-2-exo-bornanethiols from (1S)-camphor-10-thiol has been developed and the ethynyl derivatives of these thiols gave excellent diastereoselectivities in Pauson-Khand reactions with norbornene and norbornadiene through the intermediacy of a chelated dicobalt pentacarbonyl complex.
Abstract: A convenient procedure for the preparation of enantiopure 10-(R-thio)-2-exo-bornanethiols from (1S)-camphor-10-thiol has been developed. The ethynyl derivatives of these thiols gave excellent diastereoselectivities (up to 98:2) in Pauson−Khand reactions with norbornene and norbornadiene through the intermediacy of a chelated dicobalt pentacarbonyl complex. Thermal reaction conditions starting from the preformed chelated complex gave better results than N-oxide-promoted runs with in situ generation of the chelated intermediate. The corresponding adducts have been elaborated through a protocol consisting of conjugate addition, samarium iodide-promoted cleavage of the chiral auxiliary, and retro-Diels−Alder reaction to afford 4-substituted 2-cyclopentenones in high enantiomeric purity.
TL;DR: In this article, the kinetics of the ethylene-norbornene copolymerization, catalyzed by rac-Et(Ind)2ZrCl2/MAO, 90%rac/10%meso-et.
Abstract: The kinetics of the ethylene-norbornene copolymerization, catalyzed by rac-Et(Ind)2ZrCl2/MAO, 90%rac/10%meso-Et(4,7-Me2Ind)2ZrCl2/MAO and rac-H2C(3-tert-BuInd)2ZrCl2/MAO was followed by sampling from the reaction mixture at fixed time intervals. Catalyst activity, copolymer composition and molar mass were studied as a function of time. The polymers showed an unusually low polydispersity and a significant increase in their molar mass with time, suggesting a quasi-living polymerization.
TL;DR: In this article, the shielding of the double-bonded alkenes was analyzed in terms of magnetic anisotropy and steric effects of double bond together with a model (CHARGE7) for the calculation of the two-and three-branch electronic effects.
Abstract: The 1H NMR spectra of a number of alkenes of known geometry were recorded in CDCl3 solution and assigned, namely ethylene, propene, 4-methylcyclohexene, 1,4-dimethylcyclohexene, methylene cyclohexane (in CFCl3–CD2Cl2 at 153 K), 5-methylene-2-norbornene, camphene, bicyclopentadiene, styrene and 9-vinylanthracene. These results together with literature data for other alkenes, i.e. 1,3- and 1,4-cyclohexadiene, norbornene, norbornadiene, bicyclo[2.2.2]oct-2-ene and α- and β-pinene, and other data allowed the determination of the olefinic shielding in these molecules. The shielding was analysed in terms of the magnetic anisotropy and steric effects of the double bond together with a model (CHARGE7) for the calculation of the two- and three-bond electronic effects. For the aromatic alkenes ring current and π-electron effects were included. This analysis showed that the double bond shielding arises from both anisotropic and steric effects. The anisotropy is due to the perpendicular term only with a value of Δχ(CC) of −12.1 × 10−6cm3mol−1. There is also a steric deshielding term of 82.5/r6 (r in A). The shielding along the π-axis changes sign from shielding at long range (>2.5 A) to deshielding at short range (<2 A). The model gives the first comprehensive calculation of the shielding of the alkene group. For the data set considered (172 proton chemical shifts) ranging from δ=0.48 to 8.39, the r.m.s. error of observed vs calculated shifts was 0.11 ppm. Copyright © 2001 John Wiley & Sons, Ltd.