📚 Combined Analytical Techniques: MS, IR and NMR | 综合分析技术：质谱、红外与核磁共振
In Edexcel A-Level Chemistry, one of the most demanding skills is using combined analytical data to identify an unknown organic compound. Mass spectrometry (MS), infrared spectroscopy (IR) and proton NMR spectroscopy provide complementary information about molecular mass, functional groups and carbon-hydrogen environments. This article brings together the key principles, data interpretation strategies and exam techniques you need.
在爱德思 A-Level 化学中，最具挑战性的技能之一是利用综合分析数据来鉴定未知有机化合物。质谱（MS）、红外光谱（IR）和质子核磁共振（NMR）分别提供分子质量、官能团以及碳氢环境方面的互补信息。本文汇总了你需要掌握的关键原理、数据解读策略和考试技巧。
1. Why Combined Techniques Matter | 为什么需要综合技术
In structure determination, no single technique gives you the complete answer. Mass spectrometry provides the molecular ion peak (M⁺) and therefore the relative molecular mass, infrared spectroscopy identifies key functional groups, and NMR spectroscopy reveals the number and type of hydrogen environments. Exam questions normally supply data from at least two of these techniques, so you must learn to cross-check each piece of evidence.
在结构测定中，没有一种单一技术能给出完整答案。质谱提供分子离子峰（M⁺），由此得到相对分子质量；红外光谱识别关键官能团；核磁共振波谱则揭示氢环境的数目和类型。考试题通常给出至少两种技术的数据，因此你必须学会交叉核对每一项证据。
For Edexcel A-Level Chemistry, you will usually be given an empirical or molecular formula together with spectra. Your task is to assemble the fragments into a single consistent structure. This means every proposed structure must be tested against all three data sets, not just one.
在爱德思 A-Level 化学中，通常会给出实验式或分子式以及各谱图。你的任务是把各碎片拼成一个一致的结构。这意味着每一个提出的结构都必须用所有三组数据来检验，而不是只看其中一组。
2. Mass Spectrometry: Molecular Ion and Fragments | 质谱：分子离子与碎片
In a mass spectrum, the peak with the highest m/z value is usually the molecular ion, M⁺, provided no significant M+1 or M+2 peaks from isotopes confuse the picture. The m/z value of this peak equals the relative molecular mass of the compound. If the molecular ion is very small or absent, the compound may fragment easily, as with many branched alkanes and alcohols.
在质谱图中，通常最高 m/z 值的峰是分子离子峰 M⁺，前提是同位素产生的 M+1 或 M+2 峰不会造成混淆。该峰的 m/z 值等于化合物的相对分子质量。如果分子离子峰很小或不存在，则化合物可能很容易碎裂，许多支链烷烃和醇就是如此。
Fragment ions are also valuable. Common peaks include m/z 15 for CH₃⁺, m/z 29 for C₂H₅⁺ or CHO⁺, m/z 43 for C₃H₇⁺ or CH₃CO⁺, and m/z 77 for C₆H₅⁺. In addition, characteristic M+2 peaks indicate the presence of chlorine or bromine: chlorine gives about a 3:1 ratio for M⁺ to M+2, while bromine gives approximately 1:1.
碎片离子也很有价值。常见碎片峰包括 m/z 15（CH₃⁺）、m/z 29（C₂H₅⁺ 或 CHO⁺）、m/z 43（C₃H₇⁺ 或 CH₃CO⁺）和 m/z 77（C₆H₅⁺）。此外，特征的 M+2 峰指示氯或溴的存在：氯使 M⁺ 与 M+2 的比例约为 3:1，而溴约为 1:1。
3. Infrared Spectroscopy: Functional Group Fingerprints | 红外光谱：官能团指纹
Infrared spectroscopy identifies functional groups by measuring bond vibrations. Each type of bond absorbs infrared radiation at a characteristic wavenumber. For Edexcel exams, you should know the key absorption ranges: O-H in alcohols and carboxylic acids gives a broad peak around 2500–3300 cm⁻¹, C=O in aldehydes, ketones, esters and acids gives a strong sharp peak around 1680–1750 cm⁻¹, and C=C in alkenes appears around 1620–1680 cm⁻¹.
红外光谱通过测量键的振动来识别官能团。每种类型的键在特征波数处吸收红外辐射。在爱德思考试中，你应掌握关键吸收范围：醇和羧酸中的 O-H 在约 2500–3300 cm⁻¹ 处产生宽峰；醛、酮、酯和酸中的 C=O 在约 1680–1750 cm⁻¹ 处产生强尖峰；烯烃中的 C=C 出现在约 1620–1680 cm⁻¹。
It is important to distinguish between O-H in alcohols and O-H in carboxylic acids. Alcohol O-H is usually a broad, rounded absorption, while carboxylic acid O-H is even broader and overlaps with the C-H region, often extending from about 2500 to 3300 cm⁻¹. The carbonyl C=O peak confirms the presence of a carbonyl group but cannot by itself distinguish between an aldehyde, ketone, ester or acid; you need other evidence for that.
区分醇中的 O-H 和羧酸中的 O-H 很重要。醇的 O-H 通常是宽而圆润的吸收，而羧酸的 O-H 更宽，并与 C-H 区重叠，通常从约 2500 延伸到 3300 cm⁻¹。羰基 C=O 峰确认羰基的存在，但单凭它不能区分醛、酮、酯或酸；你需要其他证据。
4. Proton NMR: Chemical Shift and Integration | 质子 NMR：化学位移与积分Published by TutorHao | A-Level Revision Series | aleveler.com
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