Solid‐state complexes of poly(L‐histidine) with metal chlorides from the first row of the d‐block

Solid‐state characterization of poly(L ‐histidine) was obtained via differential scanning calorimetry, thermogravimetric analysis, optical microscopy, and infrared spectroscopy. The glass transition temperature of poly(L ‐histidine) is 169°C. This thermal transition has not been reported previously. Poly(L ‐histidine)'s T_g increases when complexes are produced with the following divalent transition metal chlorides: cobalt chloride hexahydrate, nickel chloride hexahydrate, copper chloride dihydrate, and anhydrous zinc chloride. At 10 mol % salt, nickel chloride increases T_g by 69°C. The enhancement in poly(L ‐histidine)'s T_g correlates well with ligand field stabilization energies for pseudo‐octahedral dⁿ complexes (n = 7, 8, and 10) from the first row of the d‐block. However, d⁹ copper(II) complexes do not conform to this empirical correlation. Infrared spectroscopic evidence indicates that these metal chlorides form complexes with the imidazole ring in the histidine side group and the amide group in the main chain of the polymer. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 301–309, 1999     

Conformational analysis of the disaccharide methyl α‐d‐mannopyranosyl‐(1→3)‐2‐O‐acetyl‐β‐d‐mannopyranoside monohydrate

The crystal structure of methyl α‐d ‐mannopyranosyl‐(1→3)‐2‐O‐acetyl‐β‐d ‐mannopyranoside monohydrate, C₁₅H₂₆O₁₂·H₂O, ( II ), has been determined and the structural parameters for its constituent α‐d ‐mannopyranosyl residue compared with those for methyl α‐d ‐mannopyranoside. Mono‐O‐acetylation appears to promote the crystallization of ( II ), inferred from the difficulty in crystallizing methyl α‐d ‐mannopyranosyl‐(1→3)‐β‐d ‐mannopyranoside despite repeated attempts. The conformational properties of the O‐acetyl side chain in ( II ) are similar to those observed in recent studies of peracetylated mannose‐containing oligosaccharides, having a preferred geometry in which the C2—H2 bond eclipses the C=O bond of the acetyl group. The C2—O2 bond in ( II ) elongates by ～0.02 Å upon O‐acetylation. The phi (?) and psi (ψ) torsion angles that dictate the conformation of the internal O‐glycosidic linkage in ( II ) are similar to those determined recently in aqueous solution by NMR spectroscopy for unacetylated ( II ) using the statistical program MA′AT, with a greater disparity found for ψ (Δ = ～16°) than for ? (Δ = ～6°).     

Morphology and dynamics of the poly(ϵ‐caprolactone)‐b‐poly(L‐lactide) diblock copolymer and its inclusion compound with α‐cyclodextrin: A solid‐state 13C NMR study

A biodegradable diblock copolymer of poly(ϵ‐caprolactone) (PCL) and poly(L ‐lactide) (PLLA) was synthesized and characterized. The inclusion compound (IC) of this copolymer with α‐cyclodextrin (α‐CD) was formed and characterized. Wide‐angle X‐ray diffraction showed that in the IC crystals α‐CDs were packed in the channel mode, which isolated and restricted the individual guest copolymer chains to highly extended conformation. Solid‐state ¹³C NMR techniques were used to investigate the morphology and dynamics of both the bulk and α‐CD‐IC isolated PCL‐b‐PLLA chains. The conformation of the PCL blocks isolated within the α‐CD cavities was similar to the crystalline conformation of PCL blocks in the bulk copolymer. Spin–lattice relaxation time (T₁C) measurements revealed a dramatic difference in the mobilities of the semicrystalline bulk copolymer chains and those isolated in the α‐CD‐IC channels. Carbon‐observed proton spin–lattice relaxation in the rotating frame measurements (T_1ρH) showed that the bulk copolymer was phase‐separated, while, in the IC, exchange of proton magnetization through spin‐diffusion between the isolated guest polymer chains and the host α‐CD was not complete. The two‐dimensional solid‐state heteronuclear correlation (HetCor) method was also employed to monitor proton communication in these samples. Intrablock exchange of proton magnetization was observed in both the bulk semicrystalline and IC copolymer samples at short mixing times; however, even at the longest mixing time, interblock proton communication was not observed in either sample. In spite of the physical closeness between the isolated included guest chains and the host α‐CD molecules, efficient proton spin diffusion was not observed between them in the IC. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2086–2096, 2005     

SQ—SQ experiment for determination of relative signs of small nJ(29Si,13C) couplings in a wide variety of silicon compounds

A modification of double quantum–zero quantum (DQ—ZQ) experiment termed single‐quantum–single‐quantum (SQ—SQ) experiment is proposed for the determination of relative signs and magnitudes of coupling constants. The modification replaces the multiple‐quantum evolution period by two synchronously incremented single‐quantum periods. Similarly to DQ—ZQ experiment, the sequence requires only two coupling constants that share one nucleus, the one to be measured and a reference one. This allows application to a larger variety of molecular fragments than traditional 2D sequences producing E.COSY or TROSY pattern. The SQ—SQ experiment eliminates the effects of some other couplings during t₁, thereby simplifying the 2D pattern and increasing the signal intensity in comparison with DQ—ZQ experiment. The presented sequence is particularly designed for the determination of silicon–carbon coupling constants across several bonds at natural abundance using silicon–hydrogen couplings as the sign reference. The signs of silicon–carbon couplings across two and three bonds in dimethyl(phenoxy)silane which cannot be detected by traditional methods and which have not yet been determined are established by the SQ—SQ method here: ²J(Si,C) = +2.2 Hz and ³J(Si,C) = ?1.7 Hz. Copyright © 2009 John Wiley & Sons, Ltd.     

Cucurbit[7]uril: A High‐Affinity Host for Encapsulation of Amino Saccharides and Supramolecular Stabilization of Their α‐Anomers in Water

Cucurbit[7]uril (CB[7]), an uncharged and water‐soluble macrocyclic host, binds protonated amino saccharides (D ‐glucosamine, D ‐galactosamine, D ‐mannosamine and 6‐amino‐6‐deoxy‐D ‐glucose) with excellent affinity (K_a=10³ to 10⁴ M ^?1). The host–guest complexation was confirmed by NMR spectroscopy, isothermal titration calorimetry (ITC), and MALDI‐TOF mass spectral analyses. NMR analyses revealed that the amino saccharides, except D ‐mannosamine, are bound as α‐anomers within the CB[7] cavity. ITC analyses reveal that CB[7] has excellent affinity for binding amino saccharides in water. The maximum affinity was observed for D ‐galactosamine hydrochloride (K_a=1.6×10⁴ M ^?1). Such a strong affinity for any saccharide in water using a synthetic receptor is unprecedented, as is the supramolecular stabilization of an α‐anomer by the host.     

Combination of DQ and ZQ Coherences for Sensitive Through‐Bond NMR Correlation Experiments in Biosolids under Ultra‐Fast MAS

A double‐zero quantum (DZQ)‐refocused INADEQUATE experiment is introduced for J‐based NMR correlations under ultra‐fast (60 kHz) magic angle spinning (MAS). The experiment records two spectra in the same dataset, a double quantum–single quantum (DQ‐SQ) and zero quantum–single quantum (ZQ‐SQ) spectrum, whereby the corresponding signals appear at different chemical shifts in ω₁. Furthermore, the spin‐state selective excitation (S³E) J‐decoupling block is incorporated in place of the second refocusing echo of the INADEQUATE scheme, providing an additional gain in sensitivity and resolution. The two sub‐spectra acquired in this way can be treated separately by a shearing transformation, producing two diagonal‐free single quantum (SQ‐SQ)‐type spectra, which are subsequently recombined to give an additional sensitivity enhancement, thus offering an improvement greater than a factor of two as compared to the original refocused INADEQUATE experiment. The combined DZQ scheme retains transverse magnetization on the initially polarized (I) spin, which typically exhibits a longer transverse dephasing time (T₂′) than its through‐bond neighbour (S). By doing so, less magnetization is lost during the refocusing periods in the sequence to give even further gains in sensitivity for the J correlations. The experiment is demonstrated for the correlation between the carbonyl (CO) and alpha (CA) carbons in a microcrystalline sample of fully protonated, [¹⁵N,¹³C]‐labelled Cu^II, Zn^II superoxide dismutase, and its efficiency is discussed with respect to other J‐based schemes.     

Homonuclear SQ-DQ correlations in solids: applications of the broadband BaBa scheme to reveal 31P-31P spatial correlations in two-, three-, four-, and five-spin systems

In this paper, we report on the use and limitations of the popular double‐quantum recoupling sequence back‐to‐back in studies of ³¹P‐³¹P spatial proximities in Pd‐phosphine complexes at medium field (9.38 T) under the conditions of fast MAS. The effects of internuclear distances in different spin systems and the impact of isotropic chemical shift and chemical shift anisotropy (CSA) offsets on the detectibility of SQ‐DQ correlations were of particular interest to us. Selected model compounds with these requirements in mind were synthesized. By optimization of the excitation times of SQ‐DQ correlations up to 4.6 Å could be obtained even in four‐spin systems; however, certain long‐range correlations may be weak or missing. Although under fast MAS, CSA values up to 270 ppm are well tolerated, in multi‐spin systems in cases of isotropic chemical shift offsets larger than 50 ppm, the DQ coherences cannot be properly excited. Copyright © 2011 John Wiley & Sons, Ltd.     

Darstellung,Kristallstrukturen, Schwingungsspektren und Normalkoordinatenanalysen der Tetrahalogeno‐bis‐Pyridin‐Osmium(III)‐Komplexe cis‐(n‐Bu4N)[OsCl4Py2] und trans‐(n‐Bu4N)[OsX4Py2], X = Cl,Br

Synthesis, Crystal Structures, Vibrational Spectra, and Normal Coordinate Analyses of the Tetrahalogeno‐bis‐Pyridine‐Osmium(III) Complexes cis ‐( n ‐Bu₄N)[OsCl₄Py₂] and trans ‐( n ‐Bu₄N)[OsX₄Py₂], X = Cl, Br By reaction of (n‐Bu₄N)₂[OsX₆], X = Cl, Br, with pyridine and (n‐Bu₄N)[BH₄] tetrahalogeno‐bis‐pyridine‐osmium(III) complexes are formed and purified by chromatography. X‐ray structure determinations on single crystals have been performed of cis‐(n‐Bu₄N)[OsCl₄Py₂] ( 1 ) (triclinic, space group P1, a = 9.4047(9), b = 10.8424(18), c = 17.007(2) Å, α = 71.833(2), β = 81.249(10), γ = 67.209(12)°, Z = 2), trans‐(n‐Bu₄N)[OsCl₄Py₂] ( 2 ) (orthorhombic, space group P2₁2₁2₁, a = 8.7709(12), b = 20.551(4), c = 17.174(4) Å, Z = 4) and trans‐(n‐Bu₄N)[OsBr₄Py₂] ( 3 ) (triclinic, space group P1, a = 9.132(3), b = 12.053(3), c = 15.398(2) Å, α = 95.551(18), β = 94.12(2), γ = 106.529(19)°, Z = 2). Based on the molecular parameters of the X‐ray structure determinations and assuming C₂ point symmetry for the anion of 1 and D_2h point symmetry for the anions of 2 and 3 the IR and Raman spectra are assigned by normal coordinate analysis. The valence force constants of 1 are in the Cl–Os–Cl axis f_d(OsCl) = 1.58, in the asymmetrically coordinated N′–Os–Cl ^· axes f_d(OsCl ^· ) = 1.45, f_d(OsN′) = 2.48, of 2 f_d(OsCl) = 1.62, f_d(OsN) = 2.42 and of 3 f_d(OsBr) = 1.39 and f_d(OsN) = 2.34 mdyn/Å.     

Chemical synthesis of poly‐γ‐glutamic acid by polycondensation of γ‐glutamic acid dimer: Synthesis and reaction of poly‐γ‐glutamic acid methyl ester

α‐Methyl glutamic acid (L ‐L )‐, (L ‐D )‐, (D ‐L )‐, and (D ‐D )‐γ‐dimers were synthesized from L ‐ and D ‐glutamic acids, and the obtained dimers were subjected to polycondensation with 1‐(3‐dimethylaminopropyl)‐3‐ethylcarbodiimide hydrochloride and 1‐hydroxybenzotriazole hydrate as condensation reagents. Poly‐γ‐glutamic acid (γ‐PGA) methyl ester with the number‐average molecular weights of 5000∼20,000 were obtained by polycondensation in N,N‐dimethylformamide in 44∼91% yields. The polycondensation of (L ‐L )‐ and (D ‐D )‐dimers afforded the polymers with much larger |[α]_D | compared with the corresponding dimers. The polymer could be transformed into γ‐PGA by alkaline hydrolysis or transesterification into α‐benzyl ester followed by hydrogenation. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 732–741, 2001     

Some continuous geometry transitions and the consequences for a transition‐metal atom

By considering a transition‐metal ion in the field of some symmetrically placed ions, we illustrate the consequences of a continuous change of the structure of the ligands on the energies of the 3d electrons of the transition‐metal atom. Both a rigorous mathematical derivation and an analysis based on group theory are presented. For six ions surrounding the transition‐metal atom, a continuous D_∞h → D_3d → O_h→ D_3d→ D_6d transition is observed, whereas for four ions, a continuous D_{∞ h}→ D_2d→ T_d→ D_2d→ D_4d transition results. Although the two systems possess many similarities, interesting differences are found as well. Finally, we demonstrate that when including orbital interactions between the ligands and the transition‐metal atom, quantitative differences occur. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Evaluating the Thermal Hazard of Double-Base Propellant SQ-2 by Using Microcalorimetry Method

The thermal decomposition behavior of double‐base rocket propellant SQ‐2 was studied by a Calvet microcalorimeter at four different heating rates. The kinetic and thermodynamic parameters were obtained from the analysis of the heat flow curves. The critical temperature of thermal explosion (T_b), the self acceleration decomposition temperature (T_SADT), the adiabatic decomposition temperature rise (ΔT_ad), the time‐to‐explosion of adiabatic system (t), critical temperature of hot‐spot initiation (T_cr), critical thermal explosion ambient temperature (T_acr), safety degree (SD) and thermal explosive probability (P_TE) were presented to evaluate the thermal hazard of SQ‐2.     

Phosgene‐free synthesis of polypeptides: Useful synthesis for hydrophobic polypeptides through polycondensation of activated urethane derivatives of α‐amino acids

We report a useful synthetic method of polypeptides using a series of urethane derivative of α‐amino acids (l ‐leucine, l ‐phenylalanine, l ‐valine, l ‐alanine, l ‐isoleucine, l ‐methionine), which are readily synthesized by N‐carbamoylation of tetrabutylammonium salts of α‐amino acids with diphenyl carbonate. Heating these urethane derivatives in N,N‐dimethylacetamide in the presence of n‐butylamine successfully gave the corresponding polypeptides with well‐defined structures through polycondensation with the elimination of phenol and CO₂. The matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry investigation showed that the resulting polypeptides had an n‐BuNH₂‐incorporated initiating end and an amino group at propagating end. These results strongly indicated that primary amines served as an initiator in this polycondensation system. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3726–3731     

Correlation between local mobility and mechanical properties of high‐speed melt‐spun nylon‐6 fibers

This article establishes the processing–microstructure–motion–property relationship of high‐speed melt‐spun nylon‐6 fibers. From solid‐state ¹H NMR T_1ρ (spin–lattice relaxation time in the rotating frame) relaxation studies, all nylon‐6 fibers spun at 4500–6100 m/min showed three‐component exponential decay with the time constants T_1ρ,I, T_1ρ,II, and T_1ρ,III, indicating that there existed three different motional phases. These phases were assigned to immobile crystalline, intermediate rigid amorphous, and mobile amorphous regions. The determination of the correlation time (τ_c) of the respective phases provided information about the local molecular mobility of each phase with respect to the spinning speed. As the spinning speed increased, τ_c of the crystalline region increased (4500–5200 m/min) and then reached a plateau. However, τ_c for the rigid amorphous region increased from 5200 m/min onward, indicating that the rigid amorphous chains were more oriented and constrained in the spinning speed range of 5500–6100 m/min. The drastic increase of the maximum thermal stress for all fibers from 5500 to 6100 m/min was coincident with the τ_c characteristics of the rigid amorphous region. The significant increase in tenacity and Young's modulus and the large decrease in elongation at break at 5500–6100 m/min were also in good agreement with the local molecular motion of the intermediate rigid amorphous phase in the nylon‐6 fibers. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 993–1000, 2001     

Flüssig–Flüssig‐Extraktion von Silber(I) mit Aroylthiocarbamidsäure‐O‐estern – Einfluss von Solvens und Struktur der Extragentien

Liquid–Liquid Extraction of Silver(I) with Aroylthiocarbamic‐ O ‐esters Influence of the Solvents and of the Structure of Extractants Five bisbidentate (H₂L) and two bidentate (HL) aroylthiocarbamic‐O‐esters were synthesized and used for the liquid–liquid extraction of silver(I). A silver(I) complex was characterized in solid state. The distribution ratio D_Ag and the compositions of the extracted complexes were obtained for the silver extraction from nitric acid solutions depending on the pH value and the organic solvent. D_Ag values are decreasing in the sequence of the solvents decane, decane/toluene, toluene, chloroform. The bisbidentate extractants are more effective than the bidentate ones. Hetero atoms in the bridging molecule group of the bisbidentate compounds increase the D_Ag values. The extraction behavior is discussed with regard to the calculated protonation constants and stability constants.     

Accessibility and Solid State NMR Studies on Sol‐Gel Processed Diphosphine Ligands

Novel xerogels X1 a–d were obtained by sol‐gel processing of the monomeric T‐functionalized diphosphine ligand (MeO)₃Si(CH₂)₆CH[CH₂PPh₂]₂ [1(T⁰)] with various amounts of the co‐condensing agents MeSi(OMe)₂(CH₂)₆(OMe)₂SiMe (D⁰–C₆–D⁰) and MeSi(OMe)₂(CH₂)₃(C₆H₄)(CH₂)₃(OMe)₂SiMe [Ph(1,4‐C₃D⁰)₂] . ²⁹Si CP/MAS NMR spectroscopic investigations were applied to probe the matrices and their degree of condensation. The integrity of the hydrocarbon backbone and diphosphine moiety was examined by means of solid state NMR spectroscopy (¹³C, ³¹P). To study the dynamics of the matrices and the phosphorus centers detailed measurements of relaxation time (T_1ρH) and cross polarization constants (T_SiH, T_PH) were carried out. The accessibility of the polysiloxane‐supported diphosphines was scrutinized by some typical phosphine reactions. It was found that reagents such as H₂O₂, MeI as well as bulky molecules like (NBD)Mo(CO)₄ or (COD)PdCl₂ are able to reach all phosphorus centers independent on the kind of the backbone of the matrix. SEM micrographs show the morphology of the hybrid materials and energy dispersive X‐ray spectroscopy (EDX) suggest that the distribution of the elements agree with the applied composition.     

Algebraic solutions for point groups: Cubic groups G in the group chain G⊃T⊃D2⊃C2

Concise algebraic expressions of the symmetry‐adapted functions (SAFs) for both single‐valued and double‐valued representations are derived for the group chain O⊃T⊃D₂⊃C₂ and O⊃D₄⊃D₂⊃C₂, which are functions of only the quantum numbers of the respective group chain without involving any irreducible matrix elements. It is shown that the SAFs of the cubic groups G=O,T_d,T_h,O_h can be expressed in a simple way in terms of the SAFs of the group T. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 76: 585–599, 2000     

α‐ and β‐Relaxations in neat and antiplasticized polybutadiene

Dielectric spectroscopy was carried out to measure the α‐relaxation (local segmental motion) and the higher frequency, secondary relaxation (β‐mode) in 1,4‐polybutadiene, both neat and containing a nonpolar diluent, mineral oil. The α‐relaxation shifted to lower frequencies (antiplasticization) in the presence of the diluent, suggesting the glass temperature of the latter is higher than the T_g of the polymer (i.e., >187K). The T_g of neat mineral oil cannot be determined directly, due to crystallization. While the diluent increased the magnitude of the α‐relaxation times, it had no effect on the β‐relaxation. Moreover, neither the shape of the α‐relaxation function nor its temperature dependence was influenced by the diluent. From this we conclude that the main effect of the mineral oil was to increase the local friction, without changing the degree of intermolecular cooperativity of the molecular motions. We also find that near the glass temperature, there is rough agreement between the time scale of the secondary relaxation process and the value of a noncooperative relaxation time estimated from theory. This approximate correspondence between the two relaxation times also holds for 1,2 polybutadiene. However, the β‐process cannot be identified with the noncooperative α‐relaxation, and the relationship between them is not quantitative. © 2000 John Wiley & Sons, Inc.* J Polym Sci B: Polym Phys 38: 1841–1847, 2000     

Solid state self‐assembly of the single‐walled carbon nanotubes and poly(γ‐benzyl‐l‐glutamate)s with different conformations

A series of pyrenyl‐terminated poly(γ‐benzyl‐l ‐glutamate)s (py‐PBLGs) with controlled polymer molecular weight (M_W = 2.3–14.8 kg mol^?1) and molecular weight distribution (PDI = 1.17–1.55) have been prepared from 1‐pyrenemethylamine hydrochloride‐mediated ring‐opening polymerization (ROP) of γ‐benzyl‐l ‐glutamic acid based N‐carboxyanhydride (BLG‐NCA). FTIR analysis revealed that the py‐PBLG₉ was conformationally heterogeneous with 35.0% α‐helix, 55.6% β‐sheet, and 9.4% random coil conformations in the solid state, whereas the py‐PBLG₆₆ adopts 100% α‐helix conformation. Py‐PBLGs promote the dispersion of SWCNTs in organic solvents and in the PBLG solid through π–π interaction, as evidenced by the Raman spectroscopic studies. WAXD analysis revealed that the SWCNTs significantly affect the ordering of the py‐PBLG self‐assembly: the long range hexagonal packing of py‐PBLG₆₆ rods is notably enhanced by the addition of SWCNTs, whereas the lamellar packing of py‐PGLG₉ β‐sheets is weakened. In the hexagonal lattice, the SWCNTs are intercalated parallel to the py‐PBLG₆₆ rods, in contrast to the normal orientation of the SWCNTs with respect to the extended py‐PBLG₉ chains in the β‐sheets. The relative packing structure also affects the intermolecular interaction among the PBLGs: SWCNTs promote the interaction among the py‐PBLG₉ chains packed in a lamellar structure and weaken the intermolecular interaction among the py‐PBLG₆₆ columnar hexagonal array. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4489–4497     

Pendant structure governed anion sensing property for sulfonamide‐functionalized poly(phenylacetylene)s bearing various α‐amino acids

The colorimetric detection of anionic species has been studied for α‐amino acid‐conjugated poly(phenylacetylene)s, which were prepared by the polymerization of the ethyl esters of N‐(4‐ethynylphenylsulfonyl)‐L ‐alanine, L ‐isoleucine, L ‐valine, L ‐phenylalanine, L ‐aspartic acid, and L ‐glutamic acid using Rh⁺(2,5‐norbornadiene)[(η⁶‐C₆H₅)B^?(C₆H₅)₃] as the catalyst in CHCl₃. The one‐handed helical conformations of all the sulfonamide‐functionalized polymers were characterized by Cotton effects in the circular dichroism spectra. The addition of anions with a relatively high basicity, such as tetra‐n‐butylammonium acetate and fluoride, induced drastic changes in both the optical and chiroptical properties. On the other hand, anions with a relatively low basicity, such as tetra‐n‐butylammonium nitrate, azide, and bromide, had essentially no effects on the helical conformation of all the sulfonamide‐functionalized polymers. The anion signaling property of the sulfonamide‐functionalized polymers possessing α‐amino acid moieties was significantly affected by the installed residual amino acid structures. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1683–1689, 2010     

Mechanistic Photodissociation of Glycolaldehyde: Insights from Ab Initio and RRKM Calculations

Herein we report a theoretical study on mechanistic photodissociation of glycolaldehyde, HOCH₂CHO. Equilibrium structures, transition states, and intersection structures for the α‐C? C and ‐C? H bond fissions and the β‐C? O bond fission in the excited states are determined by the complete active space self‐consistent field (CASSCF) method. Based on the CASSCF optimized structures, the potential energy profiles for the dissociations are refined by performing single‐point calculations using the multi‐state multi‐reference CASSCF second order perturbation (MS‐MR‐CASPT2) method. With a low excitation energy of 280–340 nm, the T₁ α‐C? C and β‐C? O bond fissions following intersystem crossing from the S₁ state are the predominant and comparable channels, whereas the α‐C? H bond fissions both in the S₁ and in the T₁ states are nearly prohibited due to the relevant high barriers. The rate constants for the T₁ α‐C? C and β‐C? O bond fissions are also calculated by RRKM theory. Furthermore, the S₀ reactions can occur as a consequence of intersystem crossing via T₁/S₀ intersection points resulting from the T₁ C? C and C? O bond cleavages. This photodissociation mechanism is consistent with recent experimental studies.