【正文】 ile Phenomenex. Luna C8 ( . 250mm, 5μm) 。 Ultravioletvisible Spectrometry (紫外 可見吸收光譜分析 ) Waters HPLC (W2695 pump, W2996DAD detector, automatic injector, Empower station) Column: Symmetry C18 (3. 9mm 150mm, 5μm)。 流速 mL/min。 1. Principles of UV Ee energies for electronic transition of atoms in the molecule Ev energies for vibration between two atoms Er energies for molecular rotation rve ΔΕΔΕΔΕΔΕ ++?討論： （ 1） rotational energy ΔΕr： ～ wavelength:25025?m farinfrared light Farinfrared Spectroscopy （ 2） vibrational energy ΔEv : 1 eV wavelength: 25 ?m infrared light IR （ 3） electronic energy ΔEe : 120 eV wavelength: ?m UVvis The shape of UV adsorption curve? Excitation from the ground electronic state can occur to more than one vibrational level and rotatioal sublevels. The adsorption bands are broad because each electronic energy level has multiple vibrational and rotaional energy levels associated with it. Electronic transitions P319 p, s, and n (nonbonding) electrons 167。 Examples： C H3C = OC H3? m a x 2 7 9 n m ( ? 1 5 )? m a x 2 9 1 n m ( ? 1 1 )OC H3 C HC H2= C H C HO? m a x ( R ) 3 1 5 n m ( ? 1 4 )? m a x ( R ) 3 1 9 n m ( ? 5 0 )C C H3Oacetone acrylaldehyde acetaldehyde acetophenone ii) Kband （ from German： konjuierte). It is formed byπ→π * transition in conjugated system, and the most mon band in UVvis. 特點： ① λmax 210－ 270nm， εmax＞ 10000； ② 溶劑極性 ↑時 ， λmax不變 (雙烯 )或發(fā)生紅移 (烯酮 )。 當(dāng)苯環(huán)上有發(fā)色基團取代并和苯環(huán)共軛時 ， E帶和 B帶均發(fā)生紅移 ， E2帶會和 K帶合并 。 k b cA ?abcA ?bcA ??167。 由 A=abc， 已知 b=2cm , 已求得 A=, 可得 )( 113 ?????? cmgLa(2)計算摩爾吸光系數(shù) ? 溶液中 Nb的濃度為 )( 1536????? ?? Lm o lc由 A=?bc， 已知 b=2cm , A=, 可得 )( 7 0 1145 ??????? cmm o lL?例 3 稱取純度為 %的某吸光物質(zhì) 容至 500ml，從中吸取 50ml, 于最大吸收波長處用 2cm吸收池測得透光率為 已知吸光物質(zhì)的 ?=?104, 試計算該吸光物質(zhì)的 摩爾質(zhì)量。 M + R ? MR 試液 顯色劑 有色化合物 A CR a b A CR a b A CR (a) (b) (c) 圖 (a)、 (b) 可知顯色劑濃度在 a~b 范圍內(nèi)，吸 光度比較穩(wěn)定， 因此顯色劑濃度大小要嚴格控制 在 a~b之間。選擇曲線平坦部分所對應(yīng)的 pH值作為測定 的酸度。 (5) 顯色時間 顯色反應(yīng)速度有快有慢，確定適宜顯色時間 的方法：配制一份顯色溶液，從加入顯色劑開始 每隔一定時間測吸光度一次，繪制 A—t曲線。溶劑空白只能消除溶劑、比色皿壁、溶劑界面的影響。 總之，參比液的選擇原則：使試液的吸光度 真正反映待測物的濃度。 5. Relationship between molecular structure and UV UV of Organic Compounds P348 (1)Saturated hydrocarbon pounds σ→σ * transition vacuum ultraviolet region methane (125nm)。 177nm 217nm p* p p p* p*? p? p? p p* (HOMO LVMO) ??? ?max ? Woodward and Fiesers investigated many alkene pounds, especially the terpene and steroid pounds , and an empirical formula was summarized to calculated the maximum wavelength of conjugated alkenes as followings ： ?max= ?基 +?ni?i 伍德沃德 —— 菲澤 規(guī)則 (Woodward— fieser) Heteroannular (transoid) Homoannular (cisoid) Homoannular (cisoid) Heteroannular (transoid) Parent ?=253 nm ? =217 Increments for: Double bond extending conjugation 30 30 Alkyl substituent or ring residue 5 5 Exocyclic double bond 5 5 Polar groupings: OC(O)CH3 0 0 OR 6 6 Cl, Br 5 5 NR2 60 60 SR 30 30 Example 1: Transoid: 217 nm Alkyl groups or ring residues: 3 x 5 = 15 nm Calculated: 232 nm Observed: 234 nm Transoid: 217 nm Alkyl groups ring residues: 3 x 5 = 15 nm Exocyclic double bond: 5 nm Calculated: 237 nm Observed: 235 nm Example 2: Cisoid: 253 nm Alkyl groups / ring residues: 4 x 5 = 20 nm Exocyclic double bond: 5 nm Calculated: 278 nm Observed: 275 nm Example 3: The structure of unknown pound can be confirmed by