- Let's see how to determine the number 让我们看看我们如何解决它
of expected signals in an NMR spectrum. NMR光谱中预期信号的数量。
And the best way to do this 最好的方法是看很多例子，
is just to do a lot of practice problems, 我们将从甲烷开始。
and we'll start with methane. 甲烷在同一环境中有四个质子。
Methane has four protons in the same environment. 所以我们说这四个质子
Therefore, we say those four protons 在化学上是等价的，所以我们希望看到
are chemically equivalent, and we would expect to see NMR谱中只有一个信号。
only one signal on our NMR spectrum. 所以我们期望有一个甲烷信号，
So, for methane, we would expect to see one signal, 因为所有四个质子在化学上都是等价的。
because all four protons are chemically equivalent. 如果我们用丙烷移动，碳就在这里
If we move on to propane, this carbon right here 有两个质子，这两个质子具有相同的电荷
has two protons on it, and these two protons 因此，它们在化学上是等价的
are in the same environment. 我们可以期望这两个质子有一个信号。
Therefore, they are chemically equivalent, 如果我们在这里看这些质子，
and we would expect to see only one signal 我将添加它们-这些是甲基中的质子。
for these two protons. 这些甲基质子在自己的环境中，
If we look at these protons over here, 因此我们预期这些甲基质子会有一个信号。
so let me go ahead and draw them in, 但是在这样的分子中，我们必须阅读对称性。
so these methyl protons. 我将在此处添加一行以便于查看，
These methyl protons are in their own environment here, 这三个质子与它们具有相同的环境
so we would expect one signal for these methyl protons. 因此，实际上我们有六个质子处于相同的环境。
But for a molecule like this, 这六个质子在化学上是等价的
you need to think about symmetry. 我们将期望看到全部六个信号。
So, if I draw a line right here, it's easy to see 因此，我们预计总共会有两个丙烷信号。
that these three protons 现在让我们看一下这个例子。
are in the same environment as these. 我在这里写质子。
So really, really we have six protons 我先写所有质子。
in the same environment. 我把所有的质子都放进去了吧？
So these six protons are chemically equivalent, 我们这里有这些甲基质子
and we would expect to see one signal for all six. 然后我们在那个碳上有一个质子，
So, for propane, we would expect to see 然后我们拥有所有这些质子。
a total of two signals. 他们很多。
Alright, let's move on to this one. 让我们首先关注甲基。
So let's draw in our protons here. 这些甲基质子的环境
Let's just go ahead and draw in all of them, first. 因为这种环境与这些甲基质子相同。
So we're drawing in all of the protons, alright? 它们处于同一环境中。
So we have these methyl protons here, 它们都与与质子结合的碳相邻。
and then right here, we have a proton on this carbon, 因此，我们可以期望看到所有信号。
and then we have all of these protons. 所有仙客来质子的一个信号。
So, a lot of them. 现在让我们再次考虑对称性。
Let's focus in on the methyl protons first. 让我们看一下这个分子的对称性。
These methyl protons here are in their own environment, 然后我在这里看这个质子
and that environment is the same as 与仙客来质子的环境不同。
all of these methyl protons. 但是这个环境对于这个质子是一样的。
They're all in the exact same environment. 因此，我们可以在这里期待这些红色质子的信号。
They're all right next to a carbon with a hydrogen on it. 因此，红色质子的一个信号。
And so, we would expect to see 该分子总共有两个信号。
only one signal for all these protons. 让我们来看更多示例。
So one signal for the magenta protons. 让我们看看下一个。
Alright, so again, think about symmetry. 我们这里有两个质子的碳。
Think about the symmetry of this. 这两个质子具有相同的环境。
And then, if I look at this proton right here, 它们在化学上是等价的。
right, this is in a different environment 这两个质子取决于这里的氧气。
from the magenta protons, 我们知道氧比碳更负电，
but it's in the same environment as this proton. 这样氧气将拉动电子密度。
So we would expect one signal for these red protons, here. 因此，这些质子处于不同的环境中
So, one signal for the red protons. 这两个质子中的一个
So a total of two signals for the molecule. 这两个质子在这里...
Alright, let's do some more examples. 会改变颜色...那两个红色的质子
Let's look at this one next, alright? 离氧气更远
We have a carbon right here with two protons on it. 所以他们有不同的环境。
And these two protons are in the same environment. 所以我们可以预料到红色质子的信号
They're chemically equivalent. 我们将期待黄色的质子信号。
These two protons are next to this oxygen here. 我们剩下的是甲基质子。
We know oxygen is more electronegative than carbon, 我也会添加它们。
so oxygen is going to withdraw some electron density. 在这里，这个碳有三个质子。
And so, these two protons are in a different environment 他们离氧气更远。
from these two protons. 他们有不同的环境，不是吗？它们在化学上是等价的。
These two protons right here, 因此，我们期望这些质子也有一个信号。
let me go ahead and change colors, these two protons in red 而且不要忘了这里的质子在氧气处。
are further away from the oxygen, 他在不同的环境中
so they're in a different environment. 因此我们也希望该质子有一个信号。
So we'd expect one signal from the protons in red, 如果我们全部计算在内
and we would expect one signal from the protons in yellow. 我们总共得到四个信号。
Alright, we still have our methyl protons. 我们可以期待四个信号。
Let me go ahead and draw those in. 不知道为什么将这个S放在这里，这只是一个信号。
So we have three protons over here on this carbon. 因此，对于这种酒精，我们有四个信号。
They're further away from the oxygen. 现在让我们在这里看看这种酒精。
They're in their own environment, right? 我们有两个质子吧？
They're chemically equivalent. 这些质子在这里，这些在这里。
So, one signal expected for these protons. 让我们看看它们。
Finally, don't forget about the proton right here, 对称有助于此类示例。
the proton on the oxygen. 这两个质子在同一环境中。
So, that's in its own environment, 它们在两个CH2之间，因此我们期望一个信号
so we would expect one signal for that proton. 对于那些化学上等价的质子
So, really, a total, if you count them all up, 现在，让我们看看这些质子，这些质子与一个CH2相邻。
a total of four signals. 它们也与OH相邻。
So, we would expect four signals. 它们具有与这些质子相同的环境，不是吗？
Not sure why I put an S on here, only one signal. 它们与CH2和OH相邻。
So, a total of four for this alcohol. 如果我们在这里看对称性
Let's look at this alcohol down here. 我们只能期待一个信号，
So, we have these two protons, right? 这四个质子只有一个信号。
And these protons over here, 最后，质子中留有氧气，
and these protons over here. 对称性再次帮助我们看到
So let's think about that. 该质子与该质子具有相同的环境。
Symmetry helps for an example like this. 因此，我们将期待一个信号。
These two protons are in the same environment. 在这里，我们总共有该分子的三个信号。
They're between two CH2's, so we would expect one signal 现在，让我们看看右边的化合物。
for these protons, so they're chemically equivalent. 在这里，我们看到这种碳有一个手性中心，
Let's look at these protons next, so these, right here, 因为这里也必须有氢气，
are next to a CH2. 在那个碳原子上有一个质子
They're also next to an OH. 让我们把所有这些质子放在一起
That's the exact same environment as these protons, right? 然后分析它们。
They're next to a CH2 and next to an OH. 这个碳有三个质子。
So, if you think about symmetry right here, 这个碳有两个质子。
we'd expect only one signal, 我要把它们放在粗体和虚线之间，
only one signal for these four protons. 因为我们将研究这两个质子。
And then, finally, we still have the proton on the oxygen, 然后，我们在这里有三个质子。
and once again, symmetry helps us think about the fact 现在让我们确定我们将接收多少个不同的信号。
that this proton is in the same environment as this proton, 在...之前，我将使用其他颜色...
so we would expect one signal there. 我们在这里看了CH2组，对吗？
So a total of three expected signals for this molecule. 但是这里没有手性中心，就像这里的质子一样。
Alright, let's move on to this compound 我们在该分子中没有手性中心。
over here on the right. 这两个质子在原理上是等效的。
And we can see there's a chiral center right here 但是看这里，我们这里有一个手性中心
on this carbon, and there therefore must be a hydrogen, 在这个碳上，这将影响这两个质子。
a proton, on that carbon. 这两个质子在化学上不再相等
So, let's go ahead and draw in all our protons 因为这个手性中心
and then let's analyze them, here. 基本上，如果有一个手性中心
So we have three protons on this carbon. 甲基中的两个质子CH2中的两个质子
On this carbon right here, we have two protons. 它们在原则上不等效。
And I'm drawing them in with a wedge and a dash 因此，我们将期待两个不同的信号。
because we're gonna need to think about those two protons. 这个会发出一个信号-我会用仙客来来做。
And then over here, we have three, like that. 因此，这里将有一个信号。
Alright, so let's think about 而这将发出不同的信号。
how many different signals we're going to get. 他们的环境略有不同
In the past, let me go back and use a different color, here, 因为这个手性中心
we talked about a CH2 group, right? 现在让我们继续确定
And we didn't have any chiral centers, 我们可以期望多少信号。
like these two protons right here. 这三个质子在这里
We didn't have any chiral centers in this molecule. 在化学上是等价的，它们在自己的环境中，
These two protons are, generally, equivalent. 所以我们期望这三个质子有一个信号，对吗？
But if I think about over here, I have a chiral center 这些环境与这里的环境不同，
at this carbon, and that's going to 因此我们将为他们带来信号。
affect these two protons. 在甲基中，质子总是
These two protons are no longer chemically equivalent, 在相同的环境中，它们在化学上是等价的。
alright, because a chiral center is present. 无需担心它们。
So in general, if a chiral center is present, 让我们看看这里还有什么。
the two protons on a methylene group, on a CH2 group, 我们有一个质子是氧
are generally not equivalent. 从中我们将期待一个信号。
So, we would expect two different signals. 最后，我们将...看这里选择什么颜色，
So this one might give us one signal, 我选择橙色。
and I'll put that in magenta. 在这里，我们在不同的环境中还有另一个质子，
So, one signal here. 因此我们将期望从该质子获得一个信号。
And this one, we would expect a different signal. 我们总共可以期待多少个信号？
They're in slightly different environments, 让我们数一下。
because of this chiral center that is present. 一，二，三，四，五和六。
Alright, so let's keep on going, and let's figure out 因此，这种酒精有六个预期信号。
how many more signals we would expect. 现在让我们继续到这里的苯环。
So, over here, we have these three protons 让我们看一下苯。
are chemically equivalent, and they're in their own 我们知道苯有六个质子，对吗？
unique environment, so we would expect 我在这里写下六个质子。
one signal for those three protons, alright? 所有这六个质子都在同一环境中。
And those are in a different environment 它们在化学上是等价的。
from these over here, 有时候，在这里放一个圆圈会比较容易，
so we would expect one signal for these. 这有助于我们看到这些质子是等效的。
So for a methyl group, methyl protons are always 这样可以更好地看到对称性。
in the same environment, so they're chemically equivalent. 再一次，我们看对称
So you don't have to worry about them. 所有六个质子都具有相同的环境。
And then let's see, what else do we have here? 因此，我们只会期望一个信号
We have the proton on the oxygen, NMR光谱中的苯
so we would expect one signal for that. 我会写下来。
And then, finally, we're going to have, 苯只有一个信号，
let's see, what color should I choose here, 因为所有六个质子在化学上都是等价的
let's go with orange. 现在让我们看看这个化合物。
We still have a proton right here 让我们看看我们有什么。
in its own unique environment, 我们这里有一个甲基，这里有一个甲基，
so we would expect one signal for that proton. 这是每个甲基中的三个质子。
So, how many total signals do we expect? 这些质子在同一环境中，对吗？
Let's count them up. 该甲基中的这三个质子
One, two, three, four, five, and six, 具有与这三个质子相同的环境。
so a total of six expected signals for this alcohol. 他们对氧气很满意，
Alright, let's move on to a benzene ring, here. 就在苯环旁边
Let's look at benzene. 因此对于氧和苯环。
And we know that benzene has six protons, right? 所以我们可以期待一个信号，对不对？
So I could draw in the six protons, here. 这六个质子只有一个信号。
And those six protons are all in the exact same environment. 如果我们看一下戒指，我们知道这里有一个质子。
They're all chemically equivalent. 我们知道这里有一个质子，这里也有质子。
And sometimes it's easier to just go ahead 如果我们看这些质子
and draw your circle in here, 它们都在同一环境中。
and that just helps you to see 如果我以这个质子为例...
that these protons are equivalent. 该质子取决于双键CH。
It allows you to see the symmetry a little bit better. 它也与氧结合的碳相邻。
So, again, thinking about symmetry, 和这里的环境一样吧？
all six protons are in the same environment. 这个环境与这里的环境和这里的环境完全相同，
Therefore, we would expect only one signal 所以对称又可以帮助我们看到
for benzene on an NMR spectrum. 四个质子都具有相同的环境
Let me go ahead and write that here. 它们在化学上是等价的。
So only one signal for benzene, 因此一个信号。
because all six protons are chemically equivalent. 因此，我们将期待两个信号。
Move over here to this molecule down here, alright? 我们希望在NMR光谱中看到该化合物的两个信号。
So, let's think about what we have. 最后，只是为了好玩，让我们在这里看看kuban。
We have a methyl group here, a methyl group here, 我认为这是最有趣的分子之一。
so that's three protons, 古巴有八个质子。
three protons for each methyl group. 古巴只是一个立方体。
And those protons are in the same environment, alright? 这八个质子都相等，对不对？
So, these three protons on this methyl group 如果我们看着它们，只要旋转这个立方体，
are in the same environment as these three protons. 我们将无法在此处指出区别。
They're right next to an oxygen, 我们有八个质子，都相等
which is right next to this benzene ring. 因此只有一个信号。
So, next to an oxygen next to a benzene ring. 我知道Kuban NMR仅包含一个信号。
And so, we'd expect only one signal, right? 我希望你对自己的外表有所了解
Only one signal for these six protons right here. 结构式并确定您可以预期的信号量
If you look at our ring, we know that there's a proton here. 在NMR光谱中。
We know that there's a proton here, a proton here,