📚 A-Level Chemistry June 2018 Insert 2: Core Principles | A-Level化学2018年6月插入页2核心原理
The insert provided in AQA A-Level Chemistry Paper 2 (June 2018) contains essential reference data for interpreting mass spectra, infrared spectra, and NMR spectra. Understanding the core principles behind these analytical techniques is crucial for solving structural problems in organic chemistry. This article explores the fundamental concepts that underpin each table, enabling students to apply the data effectively during examinations.
2018年6月AQA A-Level化学试卷2提供的插页包含了用于解释质谱、红外光谱和核磁共振谱的重要参考数据。理解这些分析技术背后的核心原理对于解决有机化学中的结构问题至关重要。本文探讨支撑每个数据表的基本概念，帮助学生有效运用这些数据应对考试。
1. The Role of the Insert in Organic Analysis | 插页在有机分析中的作用
In Paper 2, which focuses on organic and physical chemistry, the insert serves as a data booklet for spectroscopic and spectrometric information. It eliminates the need to memorise exact numerical values, shifting the emphasis to interpretation and logical reasoning. The tables cover mass spectrometry m/z fragments, infrared absorption frequencies, ¹³C NMR chemical shifts, and ¹H NMR chemical shifts.
在专注于有机和物理化学的试卷2中，插页充当谱学和质谱信息的数据手册。它消除了记忆精确数值的需要，将重点转向解读和逻辑推理。这些表格涵盖质谱的质荷比碎片、红外吸收频率、碳-13核磁共振化学位移以及质子核磁共振化学位移。
2. Fundamentals of Mass Spectrometry | 质谱法基本原理
Mass spectrometry determines the relative molecular mass of a compound and provides structural clues through fragmentation. In electron impact (EI) ionisation, gaseous sample molecules are bombarded with high-energy electrons, causing ejection of an electron to form a positively charged molecular ion, M•+.
质谱法通过碎片化确定化合物的相对分子质量并提供结构线索。在电子轰击电离中，气态样品分子被高能电子轰击，导致一个电子被击出，形成带正电荷的分子离子M•+。
This molecular ion can undergo further bond cleavage to produce smaller fragment ions, which are detected according to their mass-to-charge ratio (m/z). The most abundant fragment gives the base peak of the mass spectrum.
该分子离子可进一步发生键断裂，产生更小的碎片离子，这些离子根据其质荷比(m/z)被检测到。丰度最高的碎片给出质谱的基峰。
3. Molecular Ion and Fragmentation Patterns | 分子离子与碎片化模式
The molecular ion peak, often the highest m/z value in the spectrum, corresponds to the intact molecule and gives the relative molecular mass (Mr). Characteristic fragments arise from the cleavage of specific bonds, generating stable carbocations. For example, the m/z 29 peak can arise from ethyl cation (C&sub2;H&sub5;+) or formyl cation (CHO+), depending on the molecular structure.
分子离子峰通常是谱图中最高的质荷比值，对应完整分子，给出相对分子质量(Mr)。特征碎片来源于特定键的断裂，生成稳定的碳正离子。例如，m/z 29峰可能来自乙基阳离子(C&sub2;H&sub5;+)或甲酰阳离子(CHO+)，取决于分子结构。
Common fragments listed in the insert include:
插页中列出的常见碎片包括：
- m/z 15 → CH&sub3;+ (methyl cation)
- m/z 29 → C&sub2;H&sub5;+ or CHO+
- m/z 43 → C&sub3;H&sub7;+ or CH&sub3;CO+
- m/z 57 → C&sub4;H&sub9;+
- m/z 77 → C&sub6;H&sub5;+ (phenyl cation)
4. Interpreting the m/z Data Table | 解读质荷比数据表
The insert’s Table 4 lists common fragment ions and their possible origins. By examining mass spectrum peaks and matching them to this table, chemists can deduce the presence of alkyl chains, carbonyl groups, or benzene rings. It is important to consider the overall molecular formula and intensity of peaks to avoid misidentification.
插页的表4列出了常见碎片离子及其可能的来源。通过检查质谱峰并对照此表，化学家可推断出烷基链、羰基或苯环的存在。必须考虑整体分子式和峰的强度以避免错误识别。
For instance, a peak at m/z 43 could indicate a propyl fragment or an acetyl group; the surrounding peaks and IR data help distinguish them.
例如，m/z 43处的峰可能指示丙基碎片或乙酰基；周围的峰和红外数据有助于区分它们。
5. Principles of Infrared Spectroscopy | 红外光谱法原理
Infrared spectroscopy exploits the absorption of infrared radiation by covalent bonds, which undergo vibrational excitation. The frequency of absorbed radiation depends on bond strength and the masses of the bonded atoms, typically measured in wavenumbers (cm&supminus;¹). A molecule absorbs IR radiation only if the vibration leads to a change in dipole moment.
红外光谱利用共价键对红外辐射的吸收，共价键发生振动激发。吸收辐射的频率取决于键的强度和成键原子的质量，通常以波数(cm&supminus;¹)测量。只有当振动导致偶极矩变化时，分子才吸收红外辐射。
The fundamental vibrations include stretching (symmetrical and asymmetrical) and bending (scissoring, rocking, wagging, twisting). Stretching vibrations of polar bonds give the most informative absorptions for functional group identification.
基本振动包括伸缩（对称和反对称）和弯曲（剪式、摇摆、面外摇摆、扭曲）。极性键的伸缩振动为官能团鉴定提供最有用的吸收。
6. Key IR Absorptions and Functional Groups | 关键红外吸收与官能团
Table 1 in the insert gives characteristic absorption ranges for bonds in organic compounds. The exact position helps identify specific functional groups, and the fingerprint region (below 1500 cm&supminus;¹) provides a unique pattern for the molecule.
插页中的表1给出了有机化合物中键的特征吸收范围。精确位置有助于鉴定特定官能团，指纹区（低于1500 cm&supminus;¹）提供分子的独特谱图。
| Bond | Functional Group | Wavenumber range (cm&supminus;¹) |
|---|---|---|
| C=O | aldehydes, ketones, carboxylic acids, esters | 1680–1750 |
| O–H | alcohols, phenols (hydrogen-bonded) | 3200–3550 (broad) |
| C–O | alcohols, ethers, esters | 1000–1300 |
| C=C | alkenes | 1620–1680 |
| C≡C | alkynes | 2100–2260 |
| O–H | carboxylic acids (very broad) | 2500–3300 |
Note that the presence of a broad O–H peak alongside a sharp C=O peak strongly suggests a carboxylic acid.
注意，宽O–H峰与尖锐C=O峰同时出现强有力地提示羧酸的存在。
7. Understanding ¹³C NMR Spectroscopy | 理解碳-13核磁共振波谱
Nuclei such as ¹³C possess spin, which creates a magnetic moment. In an external magnetic field, these nuclei can align with or against the field, creating energy levels. Radio waves of the correct frequency cause transitions between these levels, detected as NMR signals. The precise frequency depends on the chemical environment of the carbon atom due to electron shielding, giving the chemical shift (δ in ppm).
像碳-13这样的原子核具有自旋，产生磁矩。在外磁场中，这些核可以与磁场对齐或反向对齐，形成能级。适当频率的无线电波引起能级之间的跃迁，被检测为核磁共振信号。精确频率取决于碳原子因电子屏蔽而受到的化学环境，给出化学位移（δ，单位ppm）。
Electrons around the nucleus generate a small induced magnetic field that opposes the external field, shielding the nucleus. Electronegative atoms withdraw electron density, causing deshielding and a larger δ value.
核周围的电子产生一个与外磁场方向相反的小感应磁场，屏蔽了原子核。电负性原子拉走电子密度，导致去屏蔽和更大的δ值。
8. Chemical Shifts in ¹³C NMR | 碳-13 NMR中的化学位移
Table 2 provides ¹³C chemical shift ranges. Carbons bonded to electronegative atoms like oxygen or nitrogen appear at higher δ values (downfield) because deshielding reduces electron density. For example, a carbonyl carbon (C=O) absorbs around 160–220 ppm, while an alkane carbon appears at 0–50 ppm.
表2提供了碳-13化学位移范围。与电负性原子（如氧或氮）键合的碳出现在更高的δ值（低场），因为去屏蔽降低了电子密度。例如，羰基碳(C=O)在约160–220 ppm处吸收，而烷烃碳出现在0–50 ppm。
The number of signals equals the number of non-equivalent carbon environments, providing insight into molecular symmetry. Two carbon atoms that are related by symmetry (e.g., in a plane or axis) give a single peak.
信号的数量等于非等价碳环境的数目，可洞察分子对称性。由对称性（例如对称面或对称轴）关联的两个碳原子只给出一个峰。
Typical ¹³C shifts from the insert:
- R–CH&sub3;: 5–25 ppm
- R–CH&sub2;–R: 20–45 ppm
- C attached to C=C: 100–150 ppm
- C attached to C=O: 160–220 ppm
9. Proton (¹H) NMR Spectroscopy Principles | 质子核磁共振波谱原理
Similarly, ¹H NMR detects protons in different environments. Table 3 lists chemical shift ranges for protons attached to various groups (alkyl, alkenyl, aromatic, etc.). The area under each signal (integration) is proportional to the number of equivalent protons causing that signal. Spin-spin coupling with neighbouring non-equivalent protons causes splitting of signals into multiplets, following the n+1 rule.
类似地，质子核磁共振检测不同环境中的质子。表3列出了附着在不同基团（烷基、烯基、芳基等）上质子的化学位移范围。每个信号下的面积（积分）与产生该信号的等价质子数成正比。与邻近非等价质子的自旋-自旋耦合导致信号裂分成多重峰，遵循n+1规则。
Protons in identical environments are chemically equivalent and produce one signal. For example, the three protons of a methyl group attached to a saturated carbon typically appear as a singlet if no adjacent protons exist, or are split by neighbouring protons.
相同环境中的质子是化学等价的，产生一个信号。例如，连接在饱和碳上的甲基的三个质子，若无相邻质子，通常表现为单峰，否则被邻近质子裂分。
10. Integration and Spin-Spin Splitting | 积分与自旋-自旋裂分
The integration trace is displayed as a stepped line; the relative heights correspond to proton ratios. In conjunction with the n+1 rule, the multiplicity reveals how many protons are on adjacent carbon atoms. For instance, a triplet indicates two neighbouring protons (n=2, multiplicity 3). A quartet suggests three neighbouring protons (n=3, multiplicity 4).
积分迹线显示为阶梯线；相对高度对应于质子比率。结合n+1规则，多重性揭示相邻碳原子上有多少质子。例如，一个三重峰表明有两个相邻质子（n=2，多重性为3）。一个四重峰提示有三个相邻质子（n=3，多重性为4）。
Coupled protons must be non-equivalent; equivalent protons do not split each other. Thus, a CH&sub2; group next to a CH&sub3; group gives a quartet for CH&sub2; (due to CH&sub3;) and a triplet for CH&sub3; (due to CH
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