Name: 馬爾科夫尼科夫法則 (Markovnikov's Rule)
Uploaded: 2025-04-18T07:11:39.000Z
Duration: 11 min 17 s

In this video, we're going to focus on Markovnikov's rule.

在本視頻中，我們將重點介紹馬爾科夫尼科夫法則。

So let's say we have this alkene, 2-pentene, and we react it with hydrobromic acid.

比方說，我們有一個烯烴，2-戊烯，我們將它與氫溴酸反應。

What will be the products of that reaction?

And let's compare it to if we have, let's say, 1-butene.

讓我們把它與 1-丁烯進行比較。

If we react that with HBr, what will be the major product of that reaction?

如果我們用 HBr 進行反應，反應的主要產物是什麼？

Now, for the first reaction above, we get a mixture of two different products.

現在，對於上述第一個反應，我們得到了兩種不同產物的混合物。

We're going to get 3-bromopentane and 2-bromopentane.

我們將得到 3-溴戊烷和 2-溴戊烷。

But for the reaction below, we're going to get a major product, which is 2-bromobutane.

但在下面的反應中，我們將得到一種主要產物，即 2-溴丁烷。

Now, we could get 1-bromobutane, but that's going to be a minor product.

現在，我們可以得到 1-溴丁烷，但那只是次要產品。

So the question is, why do we get this as the major product?

那麼問題來了，為什麼我們的主要產品是這個？

Well, there's something called Markovnikov's rule, which basically states that the hydrogen atom, or the electrophile, adds to the carbon with the most number of hydrogen atoms.

嗯，有一條叫做馬爾科夫尼科夫規則的東西，它基本上是說，氫原子或親電體與氫原子數最多的碳相加。

And these are the carbons that are the sp2 carbons, the carbons that are part of the alkene.

這些碳是 sp2 碳，是烯烴的一部分。

This carbon has one hydrogen, and this carbon has two hydrogens.

這個碳有一個氫，這個碳有兩個氫。

So based on Markovnikov's rule, the hydrogen is going to go on this carbon, the one with the most number of carbons, which means the halogen goes on the other carbon.

是以，根據馬爾科夫尼科夫定律，氫將會在碳數最多的這個碳上，這意味著鹵素將在另一個碳上。

So another way of looking at Markovnikov's rule is that the halogen, the bromine atom, is going to go on the more substituted carbon.

是以，馬爾科夫尼科夫定律的另一種解釋是，鹵素（即溴原子）將位於取代度較高的碳上。

This carbon is primary because it's attached to only one other carbon.

這種碳是主碳，因為它只與另一種碳相連。

This carbon is secondary because it's attached to two other carbon atoms.

這個碳是次碳，因為它與另外兩個碳原子相連。

So even though Markovnikov's rule states that the electrophile, in this case hydrogen, goes on the sp2 carbon that has the greatest number of hydrogen atoms, that rule is equivalent to saying that the halogen, Br, goes on the more substituted carbon atom.

是以，儘管馬爾科夫尼科夫法則規定，親電體（在本例中為氫原子）位於氫原子數最多的 sp2 碳上，但該法則等同於鹵素（Br）位於取代程度較高的碳原子上。

And viewing it from that perspective will help you to find the answer quickly and determine if the product is Markovnikov or anti-Markovnikov.

從這個角度來看，可以幫助您快速找到答案，並確定產品是馬爾科夫尼科夫還是反馬爾科夫尼科夫。

So you could say this reaction proceeds with Markovnikov addition.

是以可以說，這一反應是以馬爾科夫尼科夫加成法進行的。

There are some reactions that proceed with anti-Markovnikov addition.

有些反應採用反馬爾科夫尼科夫加成法。

Now the reaction on top is not regioselective, so Markovnikov's rule doesn't apply.

現在上面的反應不是區域選擇性的，是以馬爾科夫尼科夫定律並不適用。

As you can see, both of these carbons are secondary and the bromine can go on either one of those two carbons.

如您所見，這兩個碳都是二級碳，溴可以位於這兩個碳中的任何一個上。

But here there's a difference, and so this reaction's gonna be regioselective.

但這裡存在差異，是以該反應將具有區域選擇性。

The bromine will preferentially add to the secondary carbon.

Now let's talk about the mechanism of this reaction to help us understand why the hydrogen atom goes on the primary carbon.

現在讓我們來談談這個反應的機理，以幫助我們理解為什麼氫原子會出現在主碳上。

So the first thing that happens is the alkene extracts a proton from HBr.

是以，首先發生的是烯烴從 HBr 中提取一個質子。

Now if we were to put the hydrogen on the secondary carbon, this will lead to a primary carbocation, which is not stable.

現在，如果我們把氫放在仲碳上，就會產生不穩定的伯碳化物。

But if we were to put the hydrogen on the secondary, I mean on the primary carbon, this would lead to a secondary carbocation, which is more stable than a primary carbocation.

但如果我們把氫放在次碳上，我是說放在主碳上，就會產生比主碳更穩定的次碳代化合物。

And that's the reason why the hydrogen atom goes on the less substituted carbon atom, or the sp2 carbon with the most hydrogen atoms, is because it leads to a more stable carbocation intermediate.

這就是為什麼氫原子會出現在取代程度較低的碳原子或氫原子最多的 sp2 碳上的原因，因為這樣會產生更穩定的碳化中間體。

Now the last step in this reaction is that bromide reacts with the carbocation, giving us the product 2-bromobutane.

現在，該反應的最後一步是溴與碳化反應，生成 2-溴丁烷。

So that's why this particular reaction proceeds with Markovnikov addition.

這就是為什麼這種特殊反應是以馬爾科夫尼科夫加成法進行的。

It's due to the fact that we get a more stable secondary carbocation intermediate.

這是因為我們得到了更穩定的仲碳化中間體。

Now consider the following three reactions.

Let's say the first one is mercury acetate with water, followed by sodium borohydride.

比方說，首先是加水的醋酸汞，然後是硼氫化鈉。

And the second one is going to be hydroboration oxidation.

此外，我們還將在過氧化物中使用 HBr。

And let's compare that to the second one.

讓我們把它與第二個進行比較。

Compare that to using just HBr by itself.

So the first reaction, oxymercuration demercuration, that reaction proceeds with Markovnikov addition.

是以，第一個反應，即氧巰基脫巰基反應，是通過馬爾科夫尼科夫加成反應進行的。

So we're gonna add an OH group, and it's gonna go on the more substituted secondary carbon.

是以，我們要添加一個 OH 基團，將其置於取代度更高的仲碳上。

So this is gonna be the product of this reaction.

是以，這將是這一反應的產物。

Now the next reaction, hydroboration oxidation with alkenes, proceeds with anti-Markovnikov addition.

現在，下一個反應，即與烯烴的氫硼氧化反應，以反馬爾可夫尼科夫加成法進行。

So that means that the hydroxyl group is gonna go on the primary carbon, or the less substituted carbon of the two carbon atoms that are double bonded.

是以，這意味著羥基將出現在主碳上，或兩個雙鍵碳原子中取代程度較低的碳上。

Now we know that HBr proceeds with Markovnikov addition.

現在我們知道，HBr 是通過馬爾科夫尼科夫加成法進行的。

But HBr with peroxides proceeds with anti-Markovnikov addition.

但 HBr 與過氧化物的反應是反馬爾科夫尼科夫加成反應。

So it's important to know the regioselectivity of different reactions.

是以，瞭解不同反應的區域選擇性非常重要。

You need to know if a certain reaction proceeds with Markovnikov addition compared to if it proceeds with anti-Markovnikov addition.

您需要知道某個反應在馬可夫尼科夫加成法下是否進行，而在反馬可夫尼科夫加成法下是否進行。

So let's say we have three methyl, one butene, and we're gonna react it with some similar reagents.

比方說，我們有三個甲基和一個丁烯，我們要用一些類似的試劑進行反應。

The first one's gonna be mercury acetate in water followed by sodium borohydride.

第一個是水中的醋酸汞，然後是硼氫化鈉。

And then we're also gonna use hydroboration oxidation.

然後我們還要使用氫硼氧化法。

And then we're also gonna react it with water under acidic conditions, or equivalently, let me say that again, equivalently with H3O+.

然後，我們還要在酸性條件下讓它與水反應，或者等效地，讓我再說一遍，等效地與 H3O+ 反應。

So the first reaction proceeds with Markovnikov addition, just like before.

是以，與之前一樣，第一反應是通過馬爾科夫尼科夫加成法進行的。

The OH group is gonna go on the secondary carbon.

The second reaction proceeds with anti-Markovnikov addition.

第二個反應以反馬爾科夫尼科夫加成法進行。

So the OH group is gonna go on the primary carbon.

Now the third reaction is a little bit different.

And I wanna compare the third reaction with the other starting alkene that we use in a previous example.

我想把第三個反應與上一個例子中使用的另一個起始烯進行比較。

So if you were to mix one butene with H3O+, this reaction will proceed with Markovnikov addition.

是以，如果將一個丁烯與 H3O+ 混合，該反應將以馬爾可夫尼科夫加成法進行。

If you were to mix H3O+, or water and H+, with this particular alkene, the answer is different.

如果將 H3O+ 或水和 H+ 與這種特殊的烯烴混合，答案就不一樣了。

You actually get an alcohol that looks like this.

實際上，你得到的酒精是這樣的。

The OH group doesn't go on the secondary carbon, but rather it goes on the tertiary carbon.

羥基不在二級碳上，而是在三級碳上。

So you need to be careful with reactions that proceeds with Markovnikov addition, particularly the ones that are subject to rearrangements.

是以，您需要謹慎對待馬可夫尼科夫加成反應，尤其是那些可能發生重排的反應。

For the most part, the oxymercuration demercuration reaction doesn't generally proceed with rearrangements.

在大多數情況下，氧巰基脫巰基反應一般不會發生重排。

However, reactions that involve a carbocation intermediate, like the ones with HBr or H3O+, these proceed with rearrangements.

然而，涉及碳化中間體的反應，如與 HBr 或 H3O+ 的反應，則會發生重排。

And as a result, the OH group goes on the most substituted carbon that is in the vicinity of the double bond.

是以，OH 基團會進入雙鍵附近取代程度最高的碳上。

So now let's go over the mechanism of that reaction.

現在讓我們來了解一下該反應的機理。

Let's see why we get the tertiary alcohol.

讓我們來看看為什麼會有三級酒精。

So in the first step, we can react it with H3O+, or H+.

是以，第一步，我們可以讓它與 H3O+ 或 H+ 反應。

So the alkene is going to abstract a proton, and we're gonna get water.

烯會抽取一個質子，然後得到水。

Based on Markovnikov's rule, that proton is gonna go on the primary carbon, the carbon with the most number of hydrogen atoms.

根據馬爾科夫尼科夫定律，質子將進入主碳，即氫原子數最多的碳。

And now we're gonna get a secondary carbocation.

現在我們要得到一個次碳化反應。

Now, tertiary carbocations are more stable than secondary carbocations.

現在，三級碳酰基比二級碳酰基更穩定。

And molecules and ions, they like to rearrange themselves to find the most stable configuration.

分子和離子喜歡重新排列，以找到最穩定的構型。

So a hydride shift will automatically occur, and this is gonna give us a tertiary, more stable carbocation.

是以，氫化物會自動發生轉移，從而產生一個更穩定的三級碳化合物。

Once this tertiary carbocation is formed, the water molecule that we got from the previous example, I mean, from the previous step, or any other water molecule that is available, that's going to attack the carbocation.

一旦形成了這個叔碳位，我們從上一個例子中得到的水分子，我是說，從上一個步驟中得到的水分子，或者任何其他可用的水分子，都會攻擊這個碳位。

So once the nucleophile adds to the carbocation center, or the electrophile, we're gonna get this.

是以，一旦親核劑加到碳化中心或親電體上，我們就會得到這個。

Next, we need to use another water molecule to remove a hydrogen from this protonated alcohol species, or oxonium species, and then the hydrogen  And this will give us our final answer, where we have a tertiary alcohol.

接下來，我們需要用另一個水分子從質子化的醇類（或羰基）中去掉一個氫，然後再去掉氫，這樣就得到了最終答案，即三級醇。

So that's why we get that particular product.

所以，我們才會買到這種特殊的產品。

It's due to a carbocation rearrangement, and the driving force is stability.

這是由於碳位重排，其驅動力是穩定性。

Tertiary carbocations are more stable than secondary carbocations, due to the inductive effect and hyperconjugation.

由於感應效應和超共軛作用，叔碳化物比仲碳化物更穩定。

Hopefully it gave you a good introduction to Markovnikov's rule and how it works and how it applies in these scenarios.

希望這篇文章能讓你很好地瞭解馬爾科夫尼科夫法則，以及它是如何工作的，在這些情況下是如何應用的。