- A+
一般情况下，要标注耦合常数的是d，t，dd，dt，td，q峰等。dd，td，dt峰就比d，t峰情况复杂，在这种情况下首先是要确定这是哪种峰型，然后确定哪两条峰之间的差才是耦合常数。
1. d 峰：将确定两个化学位移（ppm）值相减，然后乘以相应的核磁仪器频率（如300M核磁，乘以300即可），即（A-B）* 300，化学位移标注中间值。
2. t 峰：（A-B）*核磁仪器频率。化学位移标注中间B峰的。
3. dd峰和q峰：这两种峰型容易混淆，需要注意判别。
判别方法：
1）一般从峰型上可以判断，dd峰有两种形式：一种是两组一高一矮（或4个一样高）的峰组成，另一种是三重峰，这种是因为中间的两个峰重叠了。dd峰的偶合常数有两个，大偶合是1-3=2-4，小偶合是1-2=3-4，再乘以核磁频率。
四重峰是一矮两高一矮（外面两个低,中间两个高）组成，简单判别方法是q 峰的四根线的间距一定是相等的，1-2=2-3=3-4，即只有一个偶合常数，
dd峰就是说这个H受旁边2个H的影响，裂了一次成d峰，又裂了一次成dd峰了，如苯环上的2位H 受到1位和3 位的氢影响就会形成dd峰。
实例
dd峰
J2 =（1.52693 - 1.50383）×300 =（1.49617 – 1.47307）×300 = 6.93 Hz
J1 =（1.52693 - 1.49617）×300 =（1.50383 – 1.47307）×300 = 9.23 Hz
dd峰
J1=(7.011-6.970)×400=(6.953-6.912)×400=16.4
J2=(7.011-6.953)×400=(6.970-6.912)×400=23.2
4. dt峰
特点：6 条谱线，两个明显的三重峰，积分值为1，两个偶合常数。
实例：
标注2.40 (dt, J =15.0, 2.5 Hz, 1H)
偶合常数计算法：
第二条线减去第五条线的值乘以核磁兆数(2.419-2.389) ×500=15 Hz。
(注：用第一条线减去第四条线乘以核磁兆数亦可)
用第一条线减去第二条线乘以核磁兆数 (2.424-2.419) ×500=2.5Hz
5. td 峰
特点：6 条谱线，一个明显的三重峰（三重峰的每一个峰再分裂成两个峰），积分值为1。两个偶合常数。
实例
标注：1.50 (td, J = 11.4, 6.6 Hz, 1H)
偶合常数计算方法：
用第一条线减去第三条线乘以核磁兆数(1.548-1.510) ×300=11.4 Hz
用第一条线减去第二条线乘以核磁兆数(1.548-1.526) ×300=6.6 Hz
6.ddd
特点：8条谱线，1-2=3-4=5-6=7-8
将峰从左至右分别编为1, 2, 3, 4,5,6,7,8号
1、2峰距为464.33‐460.71 =3.62 Hz J3
3、4峰距为454.70‐451.08= 3.62 Hz J3
5、6峰距为448.92‐445.30= 3.62 Hz J3
7、8峰距为439.29‐435.67= 3.62 Hz J3
1、3峰距为464.33‐454.70= 9.63 Hz J2
2、4峰距为460.71‐451.08 =9.63 Hz J2
5、7峰距为448.92‐439.29= 9.63 Hz J2
6、8峰距为445.30‐435.67= 9.63 Hz J2
2、6峰距为460.71‐445.30 =15.41Hz J1
3、7峰距为454.70‐439.29= 15.41Hz J1
来源：化学科讯
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