Name: resonance in nitrite and carbonate ions
Uploaded: 2025-05-22T09:05:33.000Z
Duration: 2 min 16 s
Channel: JoVE

大多数分子和离子可用单一的路易斯结构表示。然而，在某些化合物中，部分电子并非定域在特定的化学键或原子上，而是离域分布在多个化学键或原子之间。这类化合物需要用多个路易斯结构才能准确表示。
考虑三氧化硫的路易斯结构。每个氧原子与中心硫原子之间的单键满足了氧原子的八电子结构。然而，为了使硫原子达到完整的八电子结构，必须在硫原子与其中一个氧原子之间形成一个额外的键。
三氧化硫的这些多种路易斯结构被称为共振结构或贡献结构。所有组成原子的空间位置保持不变；然而，价电子的分布却有所不同。
这些双头箭头可视为逗号，不应与处于平衡状态的共振结构相混淆。在这些分子中，实际结构是其共振结构的加权平均值或杂化体。
共振结构通过“电子推动”来确定，即用曲线箭头表示将孤对电子转化为化学键，或将化学键转化为孤对电子，从而标示出离域区域。
这种离域作用导致共振稳定化，即分子的势能低于任何理论上的非离域结构的势能。
如果一个贡献结构的能量低于另一个，则它更接近实际的分子结构。通常采用某些规则来估计不同贡献结构之间的相对能量。
首先，所有原子均具有完整价电子层的结构更为稳定。其次，共价键数目较多的结构更为稳定。第三，能够使形式电荷最小化的结构更为稳定。
最后，负电荷位于电负性较强的原子上、正电荷位于电负性较弱的原子上的结构更为稳定。

共振和杂化结构

Resonance and Hybrid Structures

根据共振理论，如果一个分子、离子或自由基可以写出两个或多个具有相同原子排列的路易斯结构，则实际的电子分布是各个路易斯结构所示em&gt;的平均分布。


 共振结构和共振杂化


 亚硝酸根阴离子 (NO2−)的路易斯结构实际上可以用两种不同的方式绘制，通过 N–O 和 N=O 键的位置来区分。

 <img alt="Figure1" src="/files/ftp_upload/11684/11684%20PT%20Figure%201.svg" style="text-align: center; height: 50px;">

 如果亚硝酸根离子包含单键和双键，则两个键长预计会不同。 两个原子之间的双键比相同两个原子之间的单键更短（且更强）。 然而，实验表明，NO2−中的两个 N–O 键具有相同的强度和长度，并且在所有其他性质上都相同。 不可能为 NO2− 写出一个单一的路易斯结构，使得氮有一个八位组，并且两个键等价。


 相反，使用共振的概念:NO2− 中每个氮氧键中电子的实际分布是双键和单键的平均值。


 单个路易斯结构称为共振结构。 分子的实际电子结构（共振形式的平均值）称为各个共振形式的共振杂化。 路易斯结构之间的双头箭头表明它们是共振形式。

 <img alt="Figure2" src="/files/ftp_upload/11684/11684%20PT%20Figure%202.svg" style="text-align: center; height: 50px;">

 碳酸根阴离子 CO32− 提供了第二个共振例子。

 <img alt="Figure3" src="/files/ftp_upload/11684/11684%20PT%20Figure%203.svg" style="text-align: center; height: 75px;">

<ul>
 <li>一个氧原子必须有一个碳双键才能完成中心原子上的八位组。</li>
 <li>然而，所有氧原子都是等价的，并且双键可以由三个原子中的任何一个形成。 这产生了碳酸根离子的三种共振形式。</li>
 <li>由于可以写出三个相同的共振结构，因此已知碳酸根离子中电子的实际排列是三个结构的平均值。</li>
 <li>实验再次表明，所有三个C-O 键完全相同。</li>
</ul>


 被描述为共振杂化的分子从不具有由任一共振形式所描述的电子结构。 它不会在共振形式之间波动; 相反，实际的电子结构始终是所有共振形式所显示的电子结构的平均值。



本文改编自 <a href="https://openstax.org/books/chemistry-2e/pages/7-4-formal-charges-and-resonance">Openstax, Chemistry 2e, Chapter 7.4 Formal Charges and Resonance
</a>

根据共振理论，如果一种分子、离子或自由基能够写出两个或更多具有相同原子排列的路易斯结构，……

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Organic Chemistry

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Covalent Bonding and Structure

共价键与结构

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关键术语与概念

resonance in nitrite and carbonate ions

Resonance explains why some Lewis structures do not match the measured properties of a molecule or ion. When two or more Lewis structures have the same atom arrangement, the real electron distribution is an average of the structures shown.

The nitrite anion, NO2−, is one example. It can be drawn in two ways, with the N–O and N=O bonds in different places. If nitrite had one single bond and one double bond, the two bond lengths should be different, because a double bond is shorter and stronger than a single bond.

Experiments show that both N–O bonds in NO2− have the same length and strength. They are identical in all other properties as well. A single Lewis structure cannot show this and still give nitrogen an octet, so resonance is used to describe the ion.

The separate Lewis structures are called resonance structures. The true electronic structure is called a resonance hybrid, which is the average of the resonance forms. A double-headed arrow between Lewis structures shows that they are resonance forms. Nitrite does not switch back and forth between them. Its electron distribution is always the average of the forms.

The carbonate anion, CO3 2−, gives a second example. One oxygen must form a double bond to carbon to complete the octet on the central atom, but each oxygen atom is equivalent. That means the double bond can be placed with any one of the three oxygens, creating three resonance forms.

Because the three resonance structures are identical, the electron arrangement in carbonate is the average of all three. Experiments show that all three C–O bonds are exactly the same. A resonance hybrid never has the exact electronic structure of just one resonance form.

Resonance in Nitrite and Carbonate Ions

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Explore how resonance explains equal bond lengths in nitrite and carbonate ions, and learn the difference between resonance structures and a resonance hybrid.

Resonance in Nitrite and Carbonate Ions | JoVE K12

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Resonance in Nitrite and Carbonate Ions

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