质谱速查表Mass spectrometry — isotope patterns, fragments and losses
质谱仪把分子打成带正电的离子，按质荷比 m/z（离子带一个电荷时就是它的质量）分开记录。最右边的主要峰通常是分子离子峰 M⁺，给出相对分子质量；其右侧的 M+1、M+2 小峰来自 ¹³C、³⁷Cl、⁸¹Br 等重同位素；左侧的碎片峰说明分子从哪里断开。最高的那个峰叫基峰，强度定为 100%。
A mass spectrometer turns molecules into positive ions and records them by mass-to-charge ratio m/z (simply the mass for a singly charged ion). The main peak furthest right is usually the molecular ion M⁺, which gives the relative molecular mass; the small M+1 and M+2 peaks beside it come from heavier isotopes such as ¹³C, ³⁷Cl and ⁸¹Br; the fragment peaks to the left show where the molecule breaks. The tallest peak is the base peak, set to 100%.
读谱要点Reading a spectrum
碳原子数（M+1 峰）：每个碳有 1.1% 的概率是 ¹³C，所以 n = 100 × [M+1] ÷ (1.1 × [M])。例：M⁺ 相对强度 20.0，M+1 为 0.88，则 n = 100 × 0.88 ÷ (1.1 × 20.0) = 4。
Number of carbons (M+1 peak): each carbon has a 1.1% chance of being ¹³C, so n = 100 × [M+1] ÷ (1.1 × [M]). Example: M⁺ 20.0, M+1 0.88 gives n = 100 × 0.88 ÷ (1.1 × 20.0) = 4.
氯和溴（M+2 峰）：M+2 与 M 差不多高，说明有一个 Br；约为 M 的三分之一，说明有一个 Cl。两个卤素时再看 M+4（见下图）。
Chlorine and bromine (M+2 peak): an M+2 about as tall as M means one Br; about a third of M means one Cl. With two halogens look at M+4 as well (see the patterns below).
氮规则：只含 C、H、O、N、S、卤素的分子，相对分子质量为奇数时含奇数个 N，为偶数时含偶数个（或零个）N。
Nitrogen rule: for molecules containing only C, H, O, N, S and halogens, an odd relative molecular mass means an odd number of N atoms; an even mass means an even number (or none).
相对原子质量：由同位素峰计算加权平均。例：氯的两个峰 m/z 35 和 37，强度比 3 : 1，Ar = (35 × 3 + 37 × 1) ÷ 4 = 35.5。
Relative atomic mass: take the abundance-weighted mean of the isotope peaks. Example: chlorine peaks at m/z 35 and 37 in a 3 : 1 ratio give Ar = (35 × 3 + 37 × 1) ÷ 4 = 35.5.
碎片只记录带正电的那一半：M⁺ → X⁺ + Y•，看到的是 X⁺，丢掉的中性部分 Y 要从质量差推算。
Only the positively charged piece is detected: M⁺ → X⁺ + Y•. You see X⁺ and work out the lost neutral Y from the mass difference.
含卤素、硫时的同位素峰Isotope patterns of halogens and sulfur
M : M+2 ≈ 3 : 1 (³⁵Cl 75.8%, ³⁷Cl 24.2%)
M : M+2 ≈ 1 : 1 (⁷⁹Br 50.7%, ⁸¹Br 49.3%)
M : M+2 : M+4 ≈ 9 : 6 : 1
M : M+2 : M+4 ≈ 1 : 2 : 1
M : M+2 : M+4 ≈ 3 : 4 : 1
M+2 约为 M 的 4.4%（³⁴S 4.25%）
M+2 is about 4.4% of M (³⁴S 4.25%)
常见碎片离子Common fragment ions
| m/z | 离子 Ion | 说明 Notes |
|---|---|---|
| 15 | CH₃⁺ | 甲基methyl |
| 17 | OH⁺ | 羟基（醇、酸）hydroxyl (alcohols, acids) |
| 18 | H₂O⁺ | 水（常见于醇）water (often from alcohols) |
| 26 | C₂H₂⁺ | 乙炔基碎片acetylene fragment |
| 27 | C₂H₃⁺ | 乙烯基vinyl |
| 28 | CO⁺ / C₂H₄⁺ / N₂⁺ | 三者质量相同，需结合其他峰判断same nominal mass; decide from other peaks |
| 29 | C₂H₅⁺ / CHO⁺ | 乙基；醛基ethyl; formyl (aldehydes) |
| 30 | CH₂=NH₂⁺ | 伯胺的 α-断裂α-cleavage of primary amines |
| 31 | CH₂=OH⁺ | 伯醇的 α-断裂α-cleavage of primary alcohols |
| 39 | C₃H₃⁺ | 芳环、炔的碎片aromatic / alkyne fragment |
| 41 | C₃H₅⁺ | 烯丙基allyl |
| 43 | C₃H₇⁺ / CH₃CO⁺ | 丙基；乙酰基（甲基酮、乙酸酯）propyl; acetyl (methyl ketones, acetates) |
| 44 | CO₂⁺ / CH₂=CHOH⁺ | 二氧化碳；醛的麦氏重排离子CO₂; McLafferty ion of aldehydes |
| 45 | COOH⁺ / CH₃CH=OH⁺ / C₂H₅O⁺ | 羧基；仲醇碎片；乙氧基carboxyl; secondary-alcohol fragment; ethoxy |
| 57 | C₄H₉⁺ / C₂H₅CO⁺ | 叔丁基；丙酰基tert-butyl; propanoyl |
| 58 | CH₂=C(OH)CH₃⁺ | 甲基酮的麦氏重排离子McLafferty ion of methyl ketones |
| 60 | CH₂=C(OH)₂⁺ | 羧酸的麦氏重排离子McLafferty ion of carboxylic acids |
| 77 | C₆H₅⁺ | 苯基phenyl |
| 91 | C₇H₇⁺ | 苄基 / 䓬鎓离子（烷基苯的标志峰）benzyl / tropylium (marker of alkylbenzenes) |
| 105 | C₆H₅CO⁺ | 苯甲酰基benzoyl |
常见中性丢失Common neutral losses
| 峰位 Peak | 丢失 Lost | 常见于 Typical of |
|---|---|---|
| M − 1 | H• | 醛常见 M−1common for aldehydes |
| M − 15 | CH₃• | 含甲基支链methyl group present |
| M − 17 | OH• | 羧酸、醇carboxylic acids, alcohols |
| M − 18 | H₂O | 醇脱水dehydration of alcohols |
| M − 28 | CO / C₂H₄ | 酮、酚失去 CO；麦氏重排失去乙烯loss of CO from ketones and phenols; ethene from McLafferty |
| M − 29 | C₂H₅• / CHO• | 乙基；醛ethyl; aldehydes |
| M − 31 | CH₃O• | 甲酯、甲醚methyl esters and ethers |
| M − 35 | ³⁵Cl• | 氯代物（同时有 M−37）chlorides (with M−37 too) |
| M − 43 | C₃H₇• / CH₃CO• | 丙基；甲基酮propyl; methyl ketones |
| M − 44 | CO₂ | 羧酸、酯acids and esters |
| M − 45 | COOH• / C₂H₅O• | 羧酸；乙酯carboxylic acids; ethyl esters |
| M − 79 | ⁷⁹Br• | 溴代物（同时有 M−81）bromides (with M−81 too) |
各类化合物的特征What each class tends to show
| 烷烃Alkanes | M⁺ 弱，出现相差 14（CH₂）的一串峰：29、43、57、71……；支链处容易断。weak M⁺; a series 14 apart (CH₂): 29, 43, 57, 71…; breaks at branch points. |
| 醇Alcohols | M⁺ 很弱或看不到；M−18（失水）；伯醇 m/z 31。M⁺ weak or absent; M−18 (loss of water); m/z 31 for primary alcohols. |
| 醛、酮Aldehydes, ketones | α-断裂生成酰基正离子：甲基酮 m/z 43；醛 M−1、m/z 29；γ-H 存在时有麦氏重排峰（醛 44，甲基酮 58）。α-cleavage gives acylium ions: m/z 43 for methyl ketones; M−1 and m/z 29 for aldehydes; McLafferty peaks when a γ-H is present (44 for aldehydes, 58 for methyl ketones). |
| 羧酸Carboxylic acids | M−17、M−45；m/z 45（COOH⁺）；麦氏重排峰 m/z 60。M−17, M−45; m/z 45 (COOH⁺); McLafferty peak at m/z 60. |
| 酯Esters | 酰基正离子 R–C≡O⁺；甲酯 M−31，乙酯 M−45。acylium ions R–C≡O⁺; M−31 for methyl esters, M−45 for ethyl esters. |
| 胺Amines | 含一个 N 时 M⁺ 为奇数；α-断裂峰强，伯胺 m/z 30。odd M⁺ with one N; strong α-cleavage peak, m/z 30 for primary amines. |
| 卤代烃Halogen compounds | 看 M+2（见同位素图）；失去卤原子：M−35/37、M−79/81。check M+2 (see patterns); loss of halogen: M−35/37, M−79/81. |
| 芳香化合物Aromatics | M⁺ 强（环稳定）；苯环 m/z 77；烷基苯 m/z 91 常为基峰。strong M⁺ (stable ring); m/z 77 for phenyl; m/z 91 often the base peak of alkylbenzenes. |