Fluorinated tertiary alkoxides of some lanthanides: tris-trifluorotertiarybutoxides of lanthanum, praseodymium and europium

From reactions involving M{N(SiMe₃)₂}₃ (M = La, Pr and Eu) and triflurotertiary butano[(CF₃)Me₂COH; tftb.H], the compounds [La(tftb)₃(thf)_1.5] (1), [Pr(tftb)₃ (2) and [Eu(tftb)₃] (3) have been isolated. From variable temperature ¹H and ¹⁹F NMR studies it is suggested that 1 is a mixture of [La₃(tftb)₉(thf)₂] (1a) and [La₂(tftb)₆(thf)₄] (1b). X-ray crystallography has shown that 2 is the trimer [Pr₃(tftb)₉] and variable temperature ¹H and ¹⁹F NMR suggests that 3 is also a trimer, [Eu₃(tftb)₉].     

Spectral study of the structure of compartmental complexes of europium and copper

Compartmental complexes [EuH₂(fsa)₂en]Cl·3H₂O and [CuH₂(fsa)₂en]·0.5H₂O have been synthesized and characterized. The compartmental ligand (H₄(fsa)₂en) is N,N′-bis(3-carboxysalicy- lidene)ethylenediamine. Spectral study indicates that Eu(III) and Cu(II) are coordinated by the ---O₂O₂ coordinating atoms (outside) and the ---N₂O₂ coordinating atoms (inside), respectively. Since there is a considerable difference in the ligand field strength between the “outside” and “inside” coordination spheres, their different fluorescence properties have been investigated by photoacoustic spectroscopy and fluorescence spectroscopy.     

系列Cu(Ⅱ/Ⅰ)配聚物的合成、结构及光电性能

采用水热方法合成了3种Cu(Ⅱ/Ⅰ)配聚物及超分子, (1) [K₂Cu₂(ox)(btec)(MeOH)₂]_n, (2) {[Cu(pdc)(H₂O)₂]?H₂O}_n, (3) [Cu(cyan)(phen)]?H₂O (H₂ox: 草酸, H₄btec: 均苯四甲酸, MeOH: 甲醇, H₂pdc: 2, 5-吡啶二羧酸, phen: 邻菲啰啉, Hcyan: 氰尿酸). 通过X射线单晶衍射、表面光电压光谱(SPS)、固体紫外-可见(UV-Vis)、傅里叶变换红外(FTIR)光谱、元素分析等方法对配合物进行了表征. 结构解析结果表明, 配合物(1)是具有三维(3D)无限结构的配聚物; (2)是具有二维(2D)无限结构的配聚物, 但又通过氢键进一步连成了三维(3D)网络, (1)与(2)的中心金属均为Cu(II)离子; (3)为含Cu(I)的单核配合物, 但又通过氢键和π-π堆积作用, 使它成为2D超分子化合物. 配合物SPS结果显示, 配合物(1)-(3)在300-800 nm范围内都呈现光伏响应, 表明三者均具有一定的光电转换能力. 讨论了配合物的组成、结构、维数、配体种类、中心金属离子价态及配位微环境对SPS的影响,并将SPS与UV-Vis 光谱进行了关联.     

Application of potassium ferricyanide in the spectrophotometric determination of captopril

A novel method for the determination of captopril by speetrophotometer is described in this paper. The experiment is based on the fact that Fe(Ⅲ) is reduced to Fe(Ⅱ) by captopril, then the in situ formed Fe(Ⅱ) reacts with potassium ferricyanide to give the soluble prussian blue at pH 4.00, and its maximal adsorption wavelength (λmax) is 735 nm. Good linear relationship is obtained between the absorbance and the concentration of captopril in the wide range of 0.05-20 μg/mL. The linear regression equation is A = -0.04314 + 0.11423C (μg/mL) with a correlation coefficient R = 0.9998. The detection limit (3a/k) is 0.04 μg/mL, the molar absorption coefficient is 2.5×104 L/mol cm. By mensurating the absorbance of soluble prussian blue, the indirect determination of eaptopril can be obtained. This method has been successfully applied to determination of captopril in pharmaceutical samples.Analytical results obtained are satisfactory.     

Control of selected physical properties of MX solids: an experimental and theoretical investigation

A series of eight materials of stoichiometry [Pt(L-L)₂X₂][Pt(L-L)₂]Y₄ (X is Cl, Br; L-L is 1,2-diaminoethane (en) or 1,2-diaminocyclohexane (chxn); Y is ClO⁻₄, X⁻) were synthesized. Crystal structures were determined for the compounds [Pt(chxn)₂Cl₂][Pt(chxn)₂](ClO₄)₄ 1, [Pt(chxn)₂Br₂][Pt(chxn)₂](ClO₄)₄2, and [Pt(chxn)₂Br₂][Pt(chxn)₂]Br₄ 4. All three of these compounds crystallize in the orthorhombic space group I222. Compound 1 has a = 5.711(1) Å, b = 7.804(1) Å, c = 24.101(7) Å, Z = 1, d_x = 2.033 g cm⁻³. Compound 2 has a = 5.781(1) Å, b = 7.720(1) Å, c = 24.036(5) Å, Z = 1, d_x = 2.174 g cm⁻³. Compound 4 has a = 5.379(1) Å, b = 7.028(1) Å, c = 23.884(4) Å, Z = 1, d_x = 2.440 g cm⁻³. These solids contain pseudo one-dimensional chains with a charge-density-wave (CDW) ground state structure: X-Pt(IV)-X···Pt(II)···X. Single crystal resonance Raman experiments were performed on all compounds to measure the symmetric X---Pt---X stretching frequency v₁ and the band edge. It is shown that the optical and electronic properties and, therefore, the CDW strength of these one-dimensional materials may be systematically varied over a wide range by employing different combinations of L-L and Y; templates composed of hydrogen bonded networks of L-L and Y were found to control the metal-metal separation, thereby controlling the X---Pt(IV)---X…Pt(II)…X chain geometry. Relationships between the CDW strength, measured as the ratio of the short M(IV)---X distance to the long M(II)---X distance, the band gap energy v₁ and the Pt---Pt separation are developed. The reaction coordinate is found to be dominated by changes in the M---M and Pt(II)---X separations over most of the range studied, with contributions from changes in the Pt^IV---X bonds becoming important only at the smallest M---M separations. Direct evidence demonstrating that MX systems are true Peierls distorted systems is also presented. These results are consistent with modeling based on Peierls-Hubbard hamiltonians. This work explains the unusual pressure and temperature dependences that have been observed for the structures and optical properties of this class of materials and also provides a wealth of information to benchmark many-body theoretical calculations modeling electron-electron and electron-phonon interactions in one-dimensional materials.     

线型二甲基硅氧烷低聚物的制备

以八甲基环四硅氧烷(D₄)、六甲基二硅氧烷(MM)为原料, 采用固体超强酸(SA)TiO₂/SO42-为催化剂合成线型二甲基硅氧烷四聚体(MD₄M), 通过均匀设计实验和单因素实验分别研究了反应时间、反应温度、相对分子质量调节剂MM量和催化剂添加量对反应转化率和MD₄M含量的影响, 结果表明, 当D₄与MM的摩尔配比为0.75:1, 反应温度为100 ℃, 反应时间为7 h, 催化剂(SA)用量为反应物总质量的2%时, D₄开环聚合制备线型二甲基硅氧烷低聚物的反应转化率为87%, 其中MD₄M的收率为16.8%, 较硫酸催化体系提高了1.6%, 催化剂SA循环套用3次以上, 催化活性基本不变, 采用准均相体系建立了固体超强酸非均相催化D₄开环聚合的宏观动力学模型。     

DFT study on the reaction mechanisms of polyfluorosulfonate ester with F

Gas-phase reaction of C(1)F₃S(2)O₂O(3)C(4)H₂C(5)F₃ and F⁻(16) is investigated using DFT method. The geometries of various stationary points and their relative energies are obtained from 6-31+G*, 6-311G**, and 6-311++G** levels. In the S_N2(C) reaction leading to the cleavage of the C(4)–O(3) bond, the reaction complex results from attacking of F⁻ at a hydrogen atom H11 attached to carbon atom C(4). Afterward, F⁻ is attacking the atom C(4) from the backside of the atom O(3) with the help of the neighboring effect, and meanwhile a multi-membered ring, F(16)–H(11)–C(4)–C(5)–F(16), is being formed. The S_N2(C) reaction is irreversible. On the contrary, the S_N2(S) reaction leading to the cleavage of the S(2)–O(3) bond is reversible, and it is initiated by attacking of F⁻ at the atom S(2) from the backside of the atom O(3). The products of the reaction CF₃SO₃CH₂CF₃ +F⁻ should be, thermodynamically, controlled due to the reversibility of the S_N2(S) reaction, and those result, chemospecifically, from the cleavage of the C–O bond. At last, the SCRF calculations confirm that the solvent effect is preferable to the S_N2(C) reaction.     

Contribution of the cAMP-Dependent Signal Pathway to Circadian Synchrony of Motility and Resting Membrane Potential in Paramecium

It is known that the ciliated protozoan Paramecium multimicronucleatum has synchronized circadian rhythms of motility, resting membrane potential and cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine 3',5'-monophosphate (cGMP) concentrations. The present study shows that (1) extracellularly added 4 m M tetraethylammonium (TEA)⁺ (a K⁺ channel blocker) almost completely abolishes the diurnal oscillation of intracellular cAMP concentrations; (2) even 32 m^M TEA⁺ fails to abolish the circadian motility rhythm; but (3) the motility rhythm is highly damped when 4 m^M TEA⁺ and 100 μ^M CdCl₂ (a Ca²⁺ channel blocker) are added simultaneously. A cAMP analogue ( N ⁶-monobutyryl-cAMP) added extracellularly accelerates swimming velocity. Both a K⁺ channel blocker ( e.g . TEA⁺) and an inhibitor (trifluoperazine) of adenylate cyclase (AC) suppress cAMP formation, supporting the hypothesis that AC in Paramecium has dual functions, as a K⁺ channel and as an enzyme for cAMP formation. It is hypothesized that the circadian synchrony is due to circadian fluctuations of AC causing separate circadian changes both in ciliary motion and membrane potential through a cAMP-dependent signal pathway that forms a sophisticated network of second messengers to govern the synchrony together with Ca²⁺- and cGMP-dependent pathways in a manner antiphasic and/or complementary to one another.     

Formation, solution structure and reactivity of alkylperoxo complexes of titanium

A detailed in situ ¹³C and ¹H NMR spectroscopic characterization of the following families of alkylperoxo complexes of titanium is presented: Ti(η²-OOtBu)_n(OiPr)_4−n, where n = 1–4; binuclear complexes [(iPrO)₃Ti(μ-OiPr)₂Ti(OiPr)₂(η²-OOtBu)] and [(η²-OOtBu)(iPrO)₂Ti(μ-OiPr)₂Ti(OiPr)₂(η²-OOtBu)]; complexes with β-diketonato ligands: Ti(LL)₂(OEt)(η²-OOtBu), Ti(LL)₂(OiPr)(η²-OOtBu), Ti(LL)₂(η²-OOtBu)₂, Ti(LL)₂(OtBu)(η¹-OOtBu), where HLL = acetylacetone, dipivaloylmethane. These alkylperoxo complexes could not be isolated due to their instability and were studied in situ at low temperatures. Whereas the side-on (η²) coordination mode of tert-butylperoxo ligand is generally preferable, the end-on (η¹) coordination caused by spatial hindrance from surrounding bulky ligands is found in two cases. The quantitative data on the reactivity of alkylperoxo complexes found towards sulfides and alkenes were obtained. The system TiO(acac)₂/tBuOOH in C₆H₆ was reinvestigated using ¹³C and ¹H NMR spectroscopy. The structure of the complex Ti(acac)₂{CH₃C(O)(OOtBu)COO} actually formed in this system was elucidated. Four types of titanium(IV) alkylperoxo complexes were detected in the Sharpless–Katsuki catalytic system using ¹³C NMR spectroscopy.     

Heats of formation and singlet-triplet separations of hydroxymethylene and 1-hydroxyethylidene

Thermochemical parameters of hydroxymethylene (HC:OH) and 1-hydroxyethylidene (CH3C:OH) were evaluated by using coupled-cluster, CCSD(T), theory, in conjunction with the augmented correlation consistent, aug-cc-pVnZ, basis sets, with n = D, T, Q, and 5, extrapolated to the complete basis set limit. The predicted value at 298 K for Delta Hf(CH2O) is -26.0 +/- 1 kcal/mol, as compared to an experimental value of -25.98 +/- 0.01 kcal/mol, and for Delta Hf(CH:OH) it is 26.1 +/- 1 kcal/mol. The hydroxymethylene-formaldehyde energy gap is 52.1 +/- 0.5 kcal/mol, the singlet-triplet separation of hydroxymethylene is Delta E(ST)(HC:OH) = 25.3 +/- 0.5 kcal/mol, the proton affinity is PA(HC:OH) = 222.5 +/- 0.5 kcal/mol, and the ionization energy is IEa(HC:OH) = 8.91 +/- 0.04 eV. The predicted value at 298 K for Delta Hf(CH3CHO) is -39.1 +/- 1 kcal/mol as compared to an experimental value of -40.80 +/- 0.35 kcal/mol, and for Delta Hf(CH3C:OH) it is 11.2 +/- 1 kcal/mol. The hydroxyethylidene-acetaldehyde energy gap is 50.6 +/- 0.5 kcal/mol, the singlet-triplet separation of 1-hydroxyethylidene is Delta E(ST)(CH3C:OH) = 30.5 +/- 0.5 kcal/mol, the proton affinity is PA(CH3C:OH) = 234.7 +/- 0.5 kcal/mol, and the ionization energy is IEa(CH3C:OH) = 8.18 +/- 0.04 eV. The calculated energy differences between the carbene and aldehyde isomers, and, thus, the heats of formation of the carbenes, differ from the experimental values by 2.5 kcal/mol.     

Characterization of the transport properties of membranes of uncertain macroscopic structural homogeneity

The present paper confirms and extends previous applications of an original method of time-lag analysis to (concentration-independent) gas permeation through porous pellets produced by uniaxial compaction of fine graphite powder. It is shown that this approach to the study of membrane permeability enables one to (i) detect unambiguously a macroscopic structural inhomogeneity affecting transport across the membrane (often present as an unsuspected artifact of the membrane fabrication process); (ii) determine appropriate average values of the resulting space-dependent diffusion, D(x), and sorption, S(x), coefficients (without recourse to equililibrium sorption measurements); (iii) secure substantial information about the functional form, as well as the degree, of variability of D(x) and S(x); and ultimately (iv) link this information to the underlying membrane structural inhomogeneity. In the present context, the salient underlying structural feature is nonuniform porosity across the membrane, represented by (x), and the link between D(x), S(x) and (x) is provided by the simple dual-mode (intrapore gas-phase + adsorbed-phase) model of sorption and transport in porous media. The effect of increasing overall pellet porosity (_obs) by reducing applied compacting pressure, was specifically studied and found to entail marked enhancement of the degree of structural inhomogeneity without material changes in the functional form of D(x), S(x) and hence of (x). The conclusions drawn from time-lag analysis were shown to be consistent with the observed behavior of apparent diffusion coefficients derived from transient-state sorption or permeation measurements and with the results of dual-mode steady-state permeation analysis. The latter results showed additionally that, for a more complete interpretation of observed transport behavior, the variability across the pellet of the orientation of graphite particles should also be taken into account.     

The effect of substitutents on the strain energies of small ring compounds

The effect of substitutents on the strain energy (SE) of cyclic molecules is examined at the CBS, G2, and G2(MP2) levels of theory. Alkyl substitutents have a meaningful effect upon the SE of small ring compounds. gem-Dimethyl substitution lowers the strain energy of cyclopropanes, cyclobutanes, epoxides, and dimethyldioxirane (DMDO) by 6-10 kcal/mol relative to an unbranched acyclic reference molecule. The choice of the reference compound is especially important for geminal electronegative substitutents. The SE of 1,1-difluorocyclopropane is estimated to be 20.5 kcal/mol relative to acyclic reference molecule 1,3-difluoropropane but is 40.7 kcal/mol with respect to the thermodynamically more stable (DeltaE = -20.2 kcal/mol) isomeric reference compound 2,2-difluoropropane. The SE of dioxirane (DO) is estimated to be approximately 18 kcal/mol while the SE of DMDO is predicted to be approximately equal to 11 kcal/mol by using homodesmotic reactions that maintain a balanced group equivalency. The total energy (CBS-APNO) of DMDO is 2.6 kcal/mol lower than that of isomeric 1,2-dioxacyclopentane that has an estimated SE of 5 kcal/mol. The thermodynamic stability of DMDO is a consequence of its relatively strong C-H (BDE = 102.7 kcal/mol) and C-CH(3) (BDE = 98.9 kcal/mol) bonds. By comparison, the calculated sec-C-H and -C-CH(3) G2 bond dissociation energies in propane are 100.3 and 90.5 kcal/mol.     

Equilibrium constants and kinetics of carbon monoxide insertion in alkyl complexes of ruthenium(II)

The equilibrium constants of the reaction of cis, trans-[Ru(CO)₂(PMe₃)₂(CH₃)I] (Mc) with carbon monoxide to give cis, trans[Ru(CO)₂(PMe₃)₂ (COMe)i] (Ac) and trans, trans[Ru(CO)₂(PMe₃)₂(COMe)I] (At) were measured at various temperatures in toluene. The thermodynamic parameters are compared with those obtained for the isoelectronic complexes of iron, and the trend is discussed. The kinetics of the carbonylation reaction of Mc, as well as those of the inverse decarbonylation reaction of At were measured. The kinetics of the carbonylation of the new complex trans, trans-[Ru(CO)₂(PMe₃)₂(CH₃)I] (Mt) were also investigated. All the results afford further support to the previously proposed CO insertion mechanism occurring via methyl migration. The comparison of these kinetic results with those of isoelectronic complexes of iron indicates that ruthenium is more reactive than iron, which is reflected by its greater aptitude to act as catalyst in many processes.     

稀土化合物配位场理论的研究——SO(3)-Dn群的变换

本文应用唐敖庆等人的配位场理论方法,分析SO(3)-D_n群的变换,引进了D_n群不可约表示特征M的概念,统一给出了[-1]^Γ、[-1]^γ因子,SC(3)-D_n群S_mГγⁱ系数,D_n群V系数,D_n群不可约表示[Г²]和(Г²),交换因子(-1)^Г、θ(Г_MГ_MГ_M')等.并得到求SO(3)-D_n群V系数的公式,直接沟通SO(3)-D_n群链.并应用SLJГγ稀土偶合方案对EuP₅O₁₄基态谱项⁷F能谱作了分析.     

四氯化钼催化丁二烯1,2-聚合体系的紫外可见光谱研究

对四价钼系催化丁二烯1,2-聚合中Mo(Ⅳ)络合物的紫外可见光谱进行了研究.MoCl₄乙酸乙酯溶液呈棕红色,显顺磁性.在光谱的紫区和红区共有3个自旋允许d-d跃迁吸收带.Mo(Ⅳ)八面体络合物上各种配体的交换对光谱吸收带位置无影响.Mo(Ⅳ)在512nm处的特征吸收带随Al(i-Bu)₃/Mo或Al(i-Bu)₂OPh/Mo增加而渐趋消失,这是Mo(Ⅳ)→Mo(Ⅲ)反应的标志.在MoCl_4-n·(OC₈H₁₇)_n-Bd-Al(i-Bu)₂OPh₃组分陈化体系中Mo(Ⅳ)的还原得到加快,催化聚合活性亦有提高。     

Theoretical study of cyclization of 2′-hydroxychalcone

The isomerization mechanism of 2′(OH)chalcone (1) in flavanone (2) was studied. The calculations were performed with the semiempirical method AM1, using totally optimized molecular geometries. A 6-step mechanism including several equilibrium states was proposed. It was concluded that: (a) At the conformational equilibrium of 1 there could be 43.9% of s-cis conformer; (b) The acid dissociation of 1 trans-s-trans is considerable; (c) The E_E, ΔH_f and net charges show that the rotation of ring A of 1 and the formation of ring C of 2 occurs without greater impairments; (d) Although the keto structure is the most stable one, the enolate of 2 is present in the reaction medium; (e) The conversion of enol of 2 in the keto form would be the limiting step of the analyzed isomerization rate.     

一种长链烷氧基苯腙衍生物对氟离子的高选择性识别

设计并合成了一种新型长链烷氧基酰腙衍生物1-(2,4-二硝基苯基)-2-(4-(十四烷氧基)亚苄基)肼R,系统研究了受体R对9种阴离子(F^-、Cl^-、Br^-、I^-、HSO^-₄、NO^-₃、ClO^-₄、H₂PO^-₄、Ac^-)的紫外-可见吸收光谱(UV-Vis)及裸眼识别性能。 结果表明,该受体在二甲基亚砜(DMSO)体系中对F^-、Ac^-和H₂PO^-₄表现出良好的UV-Vis及裸眼识别能力。 此外,在H₂O/DMSO(体积比1∶9)体系中可对F^-实现单一UV-Vis及裸眼识别,且检出限可达7.02×10^-7 mol/L,同时制备了受体R对阴离子的检测试纸,Job曲线表明受体与阴离子形成1∶1型配合物。 F^-离子的识别机理为“氢键型”响应识别现象。     

The role of spontaneous polarization in the negative thermal expansion of tetragonal PbTiO3-based compounds

PbTiO(3)-based compounds are well-known ferroelectrics that exhibit a negative thermal expansion more or less in the tetragonal phase. The mechanism of negative thermal expansion has been studied by high-temperature neutron powder diffraction performed on two representative compounds, 0.7PbTiO(3)-0.3BiFeO(3) and 0.7PbTiO(3)-0.3Bi(Zn(1/2)Ti(1/2))O(3), whose negative thermal expansion is contrarily enhanced and weakened, respectively. With increasing temperature up to the Curie temperature, the spontaneous polarization displacement of Pb/Bi (δz(Pb/Bi)) is weakened in 0.7PbTiO(3)-0.3BiFeO(3) but well-maintained in 0.7PbTiO(3)-0.3Bi(Zn(1/2)Ti(1/2))O(3). There is an apparent correlation between tetragonality (c/a) and spontaneous polarization. Direct experimental evidence indicates that the spontaneous polarization originating from Pb/Bi-O hybridization is strongly associated with the negative thermal expansion. This mechanism can be used as a guide for the future design of negative thermal expansion of phase-transforming oxides.     

十二烷基磺酸钠对丙烯酰胺－烯丙基磺酸钠共聚物溶液粘度的影响

丙烯酞胺-烯丙基磺酸钠共聚物(PASA)优良的絮凝性能已在前文^[1]中报道.本文主要考察阴离子表面活性剂R₁₂SO₃Na对其溶液粘度的影响,并与PAM做了对照.     

合成黑索今中副产物3, 5-二硝基-1-氧-3, 5-二氮杂环己烷的晶体结构及热分解动力学

直接法硝解乌洛托品制备黑索今的过程中合成了一种新型的环形副产物,采用硅胶柱层析法分离得到3, 5-二硝基-1-氧-3, 5-二氮杂环己烷,洗脱剂为:丙酮/二氯甲烷,梯度洗脱.以丙酮为溶剂培养得到了3, 5-二硝基-1-氧-3, 5-二氮杂环己烷单晶,用元素分析、傅里叶变换红外(FTIR)光谱、核磁共振氢谱(NMR)以及质谱(MS)对其结构进行了表征,用X射线单晶衍射仪测定了其晶体结构.结果表明,晶体C₃H₆N₄O₅分子量为178.12,属于单斜晶系,空间群P121/n1,晶胞参数: a = 0.58128(13) nm, b = 1.72389(14) nm, c = 0.71072(6) nm, β =112.056°, V = 0.66006(16) nm³, Z = 4, D_C= 1.792 g·cm^-3, μ = 0.17 mm^-1, F(000) = 368.0,最终偏差因子R =0.0397.用同步热分析仪技术研究了3, 5-二硝基-1-氧-3, 5-二氮杂环己烷的热行为, DSC曲线上在383.15和519.05 K分别有一个尖锐的熔化吸热峰和分解放热峰.另外,根据Kissinger方程及Flynn-Wall-Ozawa方程和不同升温速率下的TG曲线计算得到了该化合物的热分解动力学参数(活化能和指前因子),利用Coats-Redfern法研究了该物质的热分解机理.结果表明: 3, 5-二硝基-1-氧-3, 5-二氮杂环己烷是一种低熔点、热稳定性好的化合物. Kissinger方程计算其活化能为212.32 kJ·mol^-1,指前因子为6.20×10²⁰ s^-1, Flynn-Wall-Ozawa方程计算其活化能为210.39 kJ·mol^-1,该物质的热分解动力学方程为G(α) = (1-α)^-1-1,反应级数为2.