含义Meaning
同一反应物同时经两条途径反应。产物比在整个反应中恒等于速率常数之比（动力学控制），可通过温度、催化剂改变选择性。
One reactant reacts by two routes at once. The product ratio stays equal to the rate-constant ratio throughout (kinetic control); temperature and catalysts tune selectivity.
符号说明Symbols
| 符号Symbol | 含义 Meaning | 单位 Unit |
|---|---|---|
| \(k_1, k_2\) | 两条途径的速率常数rate constants of the two channels | s⁻¹ |
推导Derivation
\(-d[\mathrm A]/dt = (k_1 + k_2)[\mathrm A]\)，总的一级衰减。
A decays with k₁ + k₂.
\(d[\mathrm B]/dt : d[\mathrm C]/dt = k_1 : k_2\)，积分后比值不变。
Formation rates are in the ratio k₁ : k₂.
选择性随温度：\(\ln(k_1/k_2) = \ln(A_1/A_2) - (E_1 - E_2)/RT\)；升温有利于活化能较大的途径。
Heating favours the channel with higher Ea.
适用条件与局限Assumptions & limitations
若产物可相互转化，长时间后转为热力学控制（产物比 = 平衡常数）。
If products interconvert, thermodynamic control takes over at long times.
例题Worked example
1,3-丁二烯加 HBr：−80 °C 主要得 1,2-加成产物（动力学控制），40 °C 主要得 1,4-产物（热力学控制）。
HBr + butadiene: 1,2-adduct at −80 °C (kinetic), 1,4-adduct at 40 °C (thermodynamic).