1、P2： Hello everyone, welcome to today s class-Organic Spectroscopic Analysis. In this lecture, we are going to learn Ultraviolet and Visible (UV-vis) Spectroscopy. Absorption of Ultraviolet and Visible Light is due to the Transition to Electrons to Higher Energy Levels. P2： 大家好，欢迎学习今天的课程 有机波谱分析。 这一节课
2、，我们将学习紫外线和可见（ UV-vis）光谱。 紫外线和可见光的吸收来源于电子能级的跃迁。 P4： The difference in energy between molecular bonding, non-bonding and anti-bonding orbitals ranges from 125-650 kJ/mole This energy corresponds to electromagnetic (EM) radiation in the ultraviolet (UV) region, 100-350 nm, and visible (VIS) regions 350
3、-700 nm of the spectrum For comparison, recall the EM spectrum， the energy of UV is higher than IR, but lower than X-ray. Using IR we observed vibrational transitions with energies of 8-40 kJ/mol at wavelengths of 2500-15,000 nm. For purposes of our discussion, we will refer to UV and VIS spectrosco
4、py as UV P4：成键，非键和反键轨道之间的能量差为 125-650 kJ / mol 该能量对应于光谱的紫外线（ UV）区域 100-350 nm 和可见光（ VIS）区域 350-700 nm 的电磁（ EM）辐射 为了进行比较，请回想 EM 光谱， UV 的能量 高于 IR，但低于 X 射线。 使用 IR，我们观察到在 2500 至 15,000 nm 波长处能量为 8-40 kJ / mol的振动跃迁。 为了便于讨论，我们将 UV 和 VIS 光谱学通称为 UV 光谱 P5： In UV spectroscopy, the sample is irradiated with th
5、e broad spectrum of the UV radiation If a particular electronic transition matches the energy of a certain band of UV, it will be absorbed The remaining UV light passes through the sample and is observed From this residual radiation a spectrum is obtained with “gaps” at these discrete energies this
6、is called an absorption spectrum P5：在紫外线光谱中，样品被紫外光照射 如果特定的电子跃迁与 某紫外线波段的能量匹配，光被吸收， 剩余的紫外线穿过样品并被观察到 从这些残余辐射中获得了在量子化能量级差的光谱 -称为吸收光谱。 P6： The lowest energy transition (and most often obs. by UV) is typically that of an electron in the Highest Occupied Molecular Orbital (HOMO) to the Lowest Unoccupied Mo
7、lecular Orbital (LUMO) P6：最低的能级跃迁（通常是通过紫外线观察）通常是最高占据分子轨道（ HOMO）到最低空轨道（ LUMO）中电子的跃迁 P7： For any bond (pair of electrons) in a molecule, the molecular orbitals are a mixture of two contributing atomic orbitals; for every bonding orbital “ created” from this mixing (, ), there is a corresponding anti-b
8、onding orbital of symmetrically higher energy (*, *) The lowest energy occupied orbitals are typically the ; likewise, the corresponding anti-bonding * orbital is of the highest energy -orbitals are of somewhat higher energy, and their complementary anti-bonding orbital somewhat lower in energy than
9、 *. Unshared pairs lie at the energy of the original atomic orbital, most often this energy is higher than or (since no bond is formed, there is no benefit in energy) P7：对于分子中的任何键（电 子对），分子轨道是两个有贡献的原子轨道的混合物；对于由该混合 (, )“创建”的每个结合轨道，都有一个对称的反能量轨道，其能量对称地较高 (*, *) 最低的能量占据轨道通常为 ；同样，相应的反键 *轨道的能量最高 -轨道的能量稍高，而
10、它们的互补反键轨道的能量比 *略低。 未成对电子对应于原始原子轨道的能量，通常该能量高于 或 于未成键，因此在能量上没变化） P8： From the molecular orbital diagram, there are several possible electronic transitions that can occur, each of a different relative energy: for example from to * transition for alkanes, to * transition for carbonyl, to * transition fo
11、r unsaturated compounds, n to * transition for O, N, S, halogens, and to * transition for carbonyl,. P8：从分子轨道图来看，可能发生几种可能的电子跃迁，每个跃迁都有不同的相对能量：烷烃 -* 跃迁，羰基 -*跃迁，不饱和化合物 - *跃迁， O， N， S，卤素 n- *跃迁，羰基从 -*过渡。 P9： Although the UV spectrum extends below 100 nm (high energy), oxygen in the atmosphere is not tra
12、nsparent below 200 nm Special equipment to study vacuum or far UV is required Routine organic UV spectra are typically collected from 200-700 nm This limits the transitions that can be observed: P9：虽然紫外线光谱延伸到 100 nm 以下（高能量），但大气中的氧气在 200 nm 以下不是透明的 需要用于研究真空或远紫外线的专用设备 常规有机 UV 光谱通常在 200-700 nm 范围内收集 这限
13、制了可以观察到的跃迁范围： P10： Unlike IR, or NMR, where there may be upwards of 5 or more resolvable peaks from which to elucidate structural information, UV tends to give wide, overlapping bands It would seem that since the electronic energy levels of a pure sample of molecules would be quantized, fine, discre
14、te bands would be observed for atomic spectra, this is the case In molecules, when a bulk sample of molecules is observed, not all bonds (pairs of electrons) are in the same vibrational or rotational energy states This effect will impact the wavelength at which a transition is observed very similar
15、to the effect of H-bonding on the O-H vibrational energy levels in neat samples 插入图 11 P10：与 IR 或 NMR 不同， UV 可能会提供 5 个或更多个可分辨峰来阐明结构信息，且 UV 往往会产生宽的重叠谱带。由于对纯分子样品的电子能级进行量子化，因此会观察到精细的分散谱带 对于原子光谱，情况就是如此 在分子中，当观察到大量分子样本时，并非所有键都处于相同的振动或旋转能态 这种影响将影响观察到跃迁的波长 -非常类似于氢键对纯净样品中O-H 振动能级的影响 P12： When these energy l
16、evels are superimposed, the effect can be readily explained any transition has the possibility of being observed P12：当这些能级叠加在一起时，效果可以很容易地解释 任何跃迁都可能被观察到 P13： In the UV spectrum, the x-axis of the spectrum is in wavelength; 200-350 nm for UV, 200-700 for UV-VIS determinations Due to the lack of any fi
17、ne structure, spectra are rarely shown in their raw form, rather, the peak maxima are simply reported as a numerical list or max P13：在紫外线光谱中，谱图的 x 轴位于波长范围内； 200-350 nm 适用于 UV， 200-700 适用于 UV-VIS 测定 由于缺 少任何精细的结构，光谱很少以其原始形式显示，而是将峰的最大值简单地报告为数值列表或 max P14： The y-axis of the spectrum is in absorbance, A
18、From the spectrometers point of view, absorbance is the inverse of transmittance: A = log10 (I0/I) From an experimental point of view, three other considerations must be made: Firstly, a long path length, Secondly, the greater the concentration, c of the sample, the more UV light will be absorbed li
19、near effect some electronic transitions are more effective at the absorption of photon than others molar absorptivity, P14：光谱的 y 轴为吸光度， A 从光谱仪的角度来看，吸光度与透射率成反比： A = log（ I / T） 从实验的角度来看，还必须考虑其他三个方面： 首先， 更长的光程 第二， 样品的浓度 c 越大，吸收的紫外线越多 线性效应 一些电子跃迁比其他跃迁更有效地吸收光子 P15： These effects are combined into the Be
20、er-Lambert Law: For most UV spectrometers, l would remain constant (standard cells are typically 1 cm in path length) concentration is typically varied depending on the strength of absorption observed or expected. molar absorptivities vary by orders of magnitude: Since path length and concentration
21、effects can be easily factored out, absorbance simply becomes proportional to , and the y-axis is sometimes expressed as directly or as the logarithm of P15：这些影响被合并到比尔 -朗伯定律中： 对于大多数紫外光谱仪， l 保持不变（标准池的路径长度通常为 1 厘米） 浓度通常根据观察到或预期的吸收强度而变化。 摩尔吸收率成数量级变化： 由于可以轻松排除光程和浓度的影响， 因此吸光度仅与 成正比，并且 y 轴有时直接表示为 或表示为 的对数
22、 P16： Practical application of UV spectroscopy are the follows: 1. UV was the first organic spectral method, however, it is rarely used as a primary method for structure determination 2. It is most useful in combination with NMR and IR data to elucidate unique electronic features that may be ambiguo
23、us in those methods 3. It can be used to assay (via max and molar absorptivity) the proper irradiation wavelengths for photochemical experiments, or the design of UV resistant paints and coatings 4. The most ubiquitous use of UV is as a detection device for HPLC; since UV is utilized for solution ph
24、ase samples vs. a reference solvent this is easily incorporated into LC design but you would need to know what compounds could and what compounds could not be detected by UV detector! So for today s lecture, we have learned about the UV spectroscopy in terms of physical principles, the spectrum and
25、applications. We ll continue to learn more about it in the next class. See you! P16：紫外光谱的实际应用如下： 紫外线 是第一种有机光谱技术，但是，它很少作为确定结构的主要方法 2.与 NMR 和 IR 数据结合使用以阐明其它方法中可能含糊不清的独特电子特征是最有用的 3.可用于（通过最大吸收波长和摩尔吸收率）测定光化学实验或设计抗紫外线的油漆和涂料的适当照射波长 4.紫外线最普遍的用途是用作 HPLC 的检测装置； 由于 UV 用于样品溶液测定，与参考溶剂对照，因此很容易与 LC 结合 但是你需要知道哪些化合物可以，哪些化合物不能被 UV 检测器检测到！ 因此，在这一节课程中，我们从原理，谱图和应用方面学习了 UV 光谱。 我们将在下一堂课中继续学习 有关它的更多信息。 再见！
