- Let's see how to determine the number -让我们看看如何确定数字
of expected signals in an NMR spectrum. NMR光谱中预期信号的分布。
And the best way to do this 最好的方法
is just to do a lot of practice problems, 只是做很多练习题，
and we'll start with methane. 我们将从甲烷开始。
Methane has four protons in the same environment. 甲烷在同一环境中有四个质子。
Therefore, we say those four protons 因此，我们说这四个质子
are chemically equivalent, and we would expect to see 在化学上是等价的，我们希望看到
only one signal on our NMR spectrum. 我们的NMR光谱中只有一个信号。
So, for methane, we would expect to see one signal, 因此，对于甲烷，我们希望看到一个信号，
because all four protons are chemically equivalent. 因为所有四个质子在化学上都是等价的。
If we move on to propane, this carbon right here 如果我们继续使用丙烷，那么这里的碳
has two protons on it, and these two protons 上面有两个质子，而这两个质子
are in the same environment. 在同一环境中。
Therefore, they are chemically equivalent, 因此，它们在化学上是等价的，
and we would expect to see only one signal 我们希望只看到一个信号
for these two protons. 对于这两个质子
If we look at these protons over here, 如果我们在这里看这些质子，
so let me go ahead and draw them in, 所以让我继续将它们吸引进去，
so these methyl protons. 这些甲基质子
These methyl protons are in their own environment here, 这些甲基质子在自己的环境中
so we would expect one signal for these methyl protons. 因此我们预期这些甲基质子会有一个信号。
But for a molecule like this, 但是对于这样的分子，
you need to think about symmetry. 您需要考虑对称性。
So, if I draw a line right here, it's easy to see 所以，如果我在这里画一条线，很容易看到
that these three protons 那三个质子
are in the same environment as these. 处于与这些相同的环境中。
So really, really we have six protons 真的，真的，我们有六个质子
in the same environment. 在相同的环境中。
So these six protons are chemically equivalent, 所以这六个质子在化学上是等价的
and we would expect to see one signal for all six. 我们希望看到所有六个信号之一。
So, for propane, we would expect to see 因此，对于丙烷，我们希望看到
a total of two signals. 总共两个信号。
Alright, let's move on to this one. 好吧，让我们继续前进。
So let's draw in our protons here. 因此，让我们在这里吸取质子。
Let's just go ahead and draw in all of them, first. 首先，让我们吸取所有这些。
So we're drawing in all of the protons, alright? 所以我们要吸收所有的质子，好吗？
So we have these methyl protons here, 所以我们这里有这些甲基质子
and then right here, we have a proton on this carbon, 然后在这里，我们在这个碳上有一个质子，
and then we have all of these protons. 然后我们拥有所有这些质子。
So, a lot of them. 所以，很多。
Let's focus in on the methyl protons first. 让我们首先关注甲基质子。
These methyl protons here are in their own environment, 这些甲基质子在自己的环境中，
and that environment is the same as 而且那个环境和
all of these methyl protons. 所有这些甲基质子。
They're all in the exact same environment. 它们都处于完全相同的环境中。
They're all right next to a carbon with a hydrogen on it. 他们就在旁边有氢的碳旁边。
And so, we would expect to see 因此，我们希望看到
only one signal for all these protons. 所有这些质子只有一个信号。
So one signal for the magenta protons. 因此，品红色质子的一个信号。
Alright, so again, think about symmetry. 好了，再来考虑对称性。
Think about the symmetry of this. 考虑一下这种对称性。
And then, if I look at this proton right here, 然后，如果我在这里看这个质子，
right, this is in a different environment 对，这是在不同的环境中
from the magenta protons, 来自洋红色质子
but it's in the same environment as this proton. 但是它和这个质子处于同一环境中
So we would expect one signal for these red protons, here. 因此，我们希望在这里为这些红色质子提供一个信号。
So, one signal for the red protons. 因此，红色质子的一个信号。
So a total of two signals for the molecule. 因此，该分子总共有两个信号。
Alright, let's do some more examples. 好吧，让我们做更多的例子。
Let's look at this one next, alright? 接下来让我们看看这个吧？
We have a carbon right here with two protons on it. 我们这里有两个质子的碳。
And these two protons are in the same environment. 而且这两个质子在同一环境中。
They're chemically equivalent. 它们在化学上是等价的。
These two protons are next to this oxygen here. 这两个质子在此氧旁边。
We know oxygen is more electronegative than carbon, 我们知道氧比碳更具负电性，
so oxygen is going to withdraw some electron density. 因此氧气将吸收一些电子密度。
And so, these two protons are in a different environment 因此，这两个质子处于不同的环境中
from these two protons. 从这两个质子
These two protons right here, 这两个质子
let me go ahead and change colors, these two protons in red 让我继续改变颜色，这两个质子为红色
are further away from the oxygen, 离氧气更远
so they're in a different environment. 因此他们处于不同的环境中。
So we'd expect one signal from the protons in red, 因此，我们希望质子发出一个红色的信号，
and we would expect one signal from the protons in yellow. 并且我们期望质子以黄色发出一个信号。
Alright, we still have our methyl protons. 好吧，我们仍然有甲基质子。
Let me go ahead and draw those in. 让我继续进行讨论。
So we have three protons over here on this carbon. 因此，我们在此碳上有三个质子。
They're further away from the oxygen. 他们远离氧气。
They're in their own environment, right? 他们在自己的环境中，对吗？
They're chemically equivalent. 它们在化学上是等价的。
So, one signal expected for these protons. 因此，这些质子有望获得一个信号。
Finally, don't forget about the proton right here, 最后，不要忘记这里的质子
the proton on the oxygen. 质子在氧气上。
So, that's in its own environment, 因此，这是在其自身的环境中，
so we would expect one signal for that proton. 因此我们希望该质子有一个信号。
So, really, a total, if you count them all up, 所以，真的，如果把它们全部算出来，
a total of four signals. 总共四个信号。
So, we would expect four signals. 因此，我们期望有四个信号。
Not sure why I put an S on here, only one signal. 不知道为什么我在这里放一个S，只有一个信号。
So, a total of four for this alcohol. 因此，一共四个这种酒精。
Let's look at this alcohol down here. 让我们在这里看看这种酒精。
So, we have these two protons, right? 那么，我们有这两个质子，对吗？
And these protons over here, 这些质子在这里
and these protons over here. 这些质子在这里
So let's think about that. 因此，让我们考虑一下。
Symmetry helps for an example like this. 对称性有助于此类示例。
These two protons are in the same environment. 这两个质子在同一环境中。
They're between two CH2's, so we would expect one signal 它们在两个CH2之间，所以我们期望一个信号
for these protons, so they're chemically equivalent. 这些质子在化学上是等价的
Let's look at these protons next, so these, right here, 接下来让我们看一下这些质子，就在这里，
are next to a CH2. 旁边是CH2。
They're also next to an OH. 它们也靠近OH。
That's the exact same environment as these protons, right? 那是与这些质子完全相同的环境，对吗？
They're next to a CH2 and next to an OH. 它们紧挨着CH2和OH。
So, if you think about symmetry right here, 因此，如果您在这里考虑对称性，
we'd expect only one signal, 我们只希望一个信号，
only one signal for these four protons. 这四个质子只有一个信号。
And then, finally, we still have the proton on the oxygen, 最后，我们仍然有质子在氧气上，
and once again, symmetry helps us think about the fact 再一次，对称性帮助我们思考事实
that this proton is in the same environment as this proton, 该质子与该质子处于同一环境中，
so we would expect one signal there. 所以我们希望那里有一个信号。
So a total of three expected signals for this molecule. 因此，该分子共有三个预期信号。
Alright, let's move on to this compound 好吧，让我们继续前进
over here on the right. 在右边的这里。
And we can see there's a chiral center right here 我们可以看到这里有一个手性中心
on this carbon, and there therefore must be a hydrogen, 在这个碳上，因此必须有氢，
a proton, on that carbon. 碳上的质子
So, let's go ahead and draw in all our protons 所以，让我们继续吸收所有的质子
and then let's analyze them, here. 然后在这里分析它们。
So we have three protons on this carbon. 因此，我们在这个碳上有三个质子。
On this carbon right here, we have two protons. 在此碳上，我们有两个质子。
And I'm drawing them in with a wedge and a dash 我用楔子和破折号画出它们
because we're gonna need to think about those two protons. 因为我们需要考虑这两个质子。
And then over here, we have three, like that. 然后在这边，我们有三个。
Alright, so let's think about 好吧，让我们考虑一下
how many different signals we're going to get. 我们将要收到多少个不同的信号。
In the past, let me go back and use a different color, here, 过去，让我回头使用另一种颜色，在这里，
we talked about a CH2 group, right? 我们讨论了CH2组，对吗？
And we didn't have any chiral centers, 而且我们没有手性中心
like these two protons right here. 就像这两个质子一样
We didn't have any chiral centers in this molecule. 我们在这个分子中没有任何手性中心。
These two protons are, generally, equivalent. 这两个质子通常是等效的。
But if I think about over here, I have a chiral center 但是如果我考虑一下这里，我有一个手性中心
at this carbon, and that's going to 在这个碳上，这将
affect these two protons. 影响这两个质子。
These two protons are no longer chemically equivalent, 这两个质子在化学上不再相等，
alright, because a chiral center is present. 好，因为存在手性中心。
So in general, if a chiral center is present, 因此，一般而言，如果存在手性中心，
the two protons on a methylene group, on a CH2 group, 在亚甲基，在CH2基上的两个质子
are generally not equivalent. 通常不相等。
So, we would expect two different signals. 因此，我们期望两个不同的信号。
So this one might give us one signal, 所以这可能给我们一个信号，
and I'll put that in magenta. 我会把它变成洋红色。
So, one signal here. 因此，这里有一个信号。
And this one, we would expect a different signal. 而这个，我们会期待一个不同的信号。
They're in slightly different environments, 他们的环境略有不同，
because of this chiral center that is present. 因为存在手性中心
Alright, so let's keep on going, and let's figure out 好吧，让我们继续前进，找出答案
how many more signals we would expect. 我们还会期望多少个信号。
So, over here, we have these three protons 所以，在这里，我们有这三个质子
are chemically equivalent, and they're in their own 在化学上是等价的，并且它们自己存在
unique environment, so we would expect 独特的环境，所以我们期望
one signal for those three protons, alright? 这三个质子一个信号，好吗？
And those are in a different environment 那些在不同的环境中
from these over here, 从这里
so we would expect one signal for these. 因此我们期望这些信号之一。
So for a methyl group, methyl protons are always 因此对于甲基，甲基质子总是
in the same environment, so they're chemically equivalent. 在相同的环境中，因此它们在化学上是等效的。
So you don't have to worry about them. 因此，您不必担心它们。
And then let's see, what else do we have here? 然后让我们看看，我们在这里还有什么？
We have the proton on the oxygen, 我们的质子上有氧气，
so we would expect one signal for that. 所以我们希望有一个信号。
And then, finally, we're going to have, 然后，最后，我们将拥有
let's see, what color should I choose here, 让我们看看，我应该在这里选择什么颜色，
let's go with orange. 我们一起去桔子吧。
We still have a proton right here 我们这里还有一个质子
in its own unique environment, 在自己独特的环境中
so we would expect one signal for that proton. 因此我们希望该质子有一个信号。
So, how many total signals do we expect? 那么，我们期望多少信号呢？
Let's count them up. 让我们数一数。
One, two, three, four, five, and six, 一，二，三，四，五和六
so a total of six expected signals for this alcohol. 因此总共有六种预期的酒精信号。
Alright, let's move on to a benzene ring, here. 好吧，让我们继续前进到苯环。
Let's look at benzene. 让我们看一下苯。
And we know that benzene has six protons, right? 而且我们知道苯有六个质子，对吗？
So I could draw in the six protons, here. 所以我可以在这里吸取六个质子。
And those six protons are all in the exact same environment. 那六个质子都在完全相同的环境中。
They're all chemically equivalent. 它们在化学上都是等效的。
And sometimes it's easier to just go ahead 有时候继续前进会更容易
and draw your circle in here, 在这里画个圆圈
and that just helps you to see 那只会帮助你看到
that these protons are equivalent. 这些质子是等效的
It allows you to see the symmetry a little bit better. 它使您可以更好地看到对称性。
So, again, thinking about symmetry, 因此，再次考虑对称性，
all six protons are in the same environment. 所有六个质子都在同一环境中。
Therefore, we would expect only one signal 因此，我们只期望一个信号
for benzene on an NMR spectrum. NMR谱上的苯。
Let me go ahead and write that here. 让我继续在这里写下。
So only one signal for benzene, 所以只有一个苯信号
because all six protons are chemically equivalent. 因为所有六个质子在化学上都是等价的
Move over here to this molecule down here, alright? 移到这里到这个分子下面，好吗？
So, let's think about what we have. 因此，让我们考虑一下我们所拥有的。
We have a methyl group here, a methyl group here, 我们这里有一个甲基，这里有一个甲基，
so that's three protons, 那是三个质子
three protons for each methyl group. 每个甲基三个质子。
And those protons are in the same environment, alright? 这些质子在相同的环境中，好吗？
So, these three protons on this methyl group 所以，这三个质子在这个甲基上
are in the same environment as these three protons. 与这三个质子处于同一环境中
They're right next to an oxygen, 他们就在氧气旁边
which is right next to this benzene ring. 就在这个苯环旁边
So, next to an oxygen next to a benzene ring. 因此，在氧旁边是苯环。
And so, we'd expect only one signal, right? 因此，我们期望只有一个信号，对吗？
Only one signal for these six protons right here. 这六个质子只有一个信号。
If you look at our ring, we know that there's a proton here. 如果您看我们的戒指，我们知道这里有一个质子。
We know that there's a proton here, a proton here, 我们知道这里有一个质子，这里有一个质子，
and a proton here. 还有一个质子
And, if we think about those protons, 而且，如果我们考虑这些质子，
they're all in the exact same environment. 它们都处于完全相同的环境中。
So if I think about, let's say, this proton. 因此，如果我考虑一下这个质子。
This proton is next to CH with a double bond. 该质子紧靠双键的CH。
It's next to a carbon right here with an oxygen. 它旁边是带有氧气的碳。
This is in the same environment as this one, right? 与这个环境处于同一环境，对吗？
This one's in the exact same environment this one is, 这个人和这个人在完全相同的环境中
this one is, so again, symmetry helps you realize 同样，对称可以帮助您实现
that all four protons are in the same environment. 所有四个质子都在同一环境中
They're chemically equivalent. 它们在化学上是等价的。
Therefore, one signal. 因此，一个信号。
So, we would expect to see two signals. 因此，我们希望看到两个信号。
We would expect to see two signals 我们希望看到两个信号
for this molecule on an NMR spectrum. 在NMR谱上的分子。
Finally, let's just, for fun, 最后，我们只是为了好玩，
let's just look at cubane, here. 让我们在这里看看古巴。
So one of the most interesting molecules, in my opinion. 我认为，这是最有趣的分子之一。
There are eight protons on cubane. 古巴有八个质子。
Cubane is just this cube here. 古巴就是这里的一个立方体。
And these eight protons are all equivalent, right? 这八个质子都相等，对吗？
So if you think about it, if you just rotated this cube, 因此，如果您考虑一下，只要旋转此立方体，
you wouldn't be able to tell the difference, here. 您将无法在此处分辨出差异。
So we have eight protons, all equivalent, 所以我们有八个质子，都相等
therefore only one signal. 因此只有一个信号。
So, cubane's NMR should have only one signal on it. 因此，古巴的NMR应该只有一个信号。
So that's hopefully some insight into how to look at 希望这对如何看待有一些见解
a dot structure, and how to figure out 点结构，以及如何计算
how many signals you would expect to see 您希望看到多少个信号
on your NMR spectrum. 在您的NMR光谱上