Введение
Триплетное состояние молекулы диоксигена
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| ImageFile = Triplet dioxygen. png
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| OtherNames =
| IUPACName = Triplet oxygen
| SystematicName = Dioxidanediyl (substitutive)
dioxygen(2•)(triplet) it is more stable as a triplet than a singlet. According to molecular orbital theory, the electron configuration of triplet oxygen has two electrons occupying two π molecular orbitals (MOs) of equal energy (that is, degenerate MOs). In accordance with Hund's rules, they remain unpaired and spin parallel, which accounts for the paramagnetism of molecular oxygen. These half filled orbitals are antibonding in character, reducing the overall bond order of the molecule to 2 from the maximum value of 3 that would occur when these antibonding orbitals remain fully unoccupied, as in dinitrogen. The molecular term symbol for triplet oxygen is 3Σ. Spin
The s = spins of the two electrons in degenerate orbitals gives rise to 2 × 2 = 4 independent spin states in total. Exchange interaction splits these into a singlet state (total spin S = 0) and a set of 3 degenerate triplet states (S = 1). In agreement with Hund's rules, the triplet states are energetically more favorable, and correspond to the ground state of the molecule with a total electron spin of S = 1. Excitation to the S = 0 state results in much more reactive, metastable singlet oxygen. Lewis structure
Because the molecule in its ground state has a non zero spin magnetic moment, oxygen is paramagnetic; i. e., it can be attracted to the poles of a magnet. Thus, the Lewis structure O=O with all electrons in pairs does not accurately represent the nature of the bonding in molecular oxygen. However, the alternative structure •O–O• is also inadequate, since it implies single bond character, while the experimentally determined bond length of 121 pm is much shorter than the single bond in hydrogen peroxide (HO–OH) which has a length of 147.5 pm. This indicates that triplet oxygen has a higher bond order. Molecular orbital theory must be used to correctly account for the observed paramagnetism and short bond length simultaneously. Under a molecular orbital theory framework, the oxygen oxygen bond in triplet dioxygen is better described as one full σ bond plus two π half bonds, each half bond accounted for by two center three electron (2c 3e) bonding, to give a net bond order of two (1+2×), while also accounting for the spin state (S'' = 1). In the case of triplet dioxygen, each 2c 3e bond consists of two electrons in a πu bonding orbital and one electron in a πg antibonding orbital to give a net bond order contribution of
The usual rules for constructing Lewis structures must be modified to accommodate molecules like triplet dioxygen or nitric oxide that contain 2c 3e bonds. There is no consensus in this regard; Pauling has suggested the use of three closely spaced collinear dots to represent the three electron bond (see illustration).
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| ImageFile = Triplet dioxygen.png
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| OtherNames =
| IUPACName = Триплетный кислород
| SystematicName = Диоксиданидил (заместительный) диоксиген(2•)(триплет) более стабилен в триплетном состоянии, чем в синглетном. Согласно теории молекулярных орбиталей, электронная конфигурация триплетного кислорода содержит два электрона, занимающих две π-молекулярные орбитали (МО) одинаковой энергии (то есть вырожденные МО). В соответствии с правилами Хунда, они остаются неспаренными и с параллельными спинами, что объясняет парамагнетизм молекулярного кислорода. Эти частично заполненные орбитали имеют антисвязывающий характер, уменьшая общий порядок связи молекулы до 2 по сравнению с максимальным значением 3, которое наблюдается, когда эти антисвязывающие орбитали остаются полностью незаполненными, как в динитрогене. Молекулярный терм-символ триплетного кислорода – 3Σ. Спин
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| Name =
| ImageFile = Triplet dioxygen. png
| ImageFile3 =
| OtherNames =
| IUPACName = Triplet oxygen
| SystematicName = Dioxidanediyl (substitutive)
dioxygen(2•)(triplet) it is more stable as a triplet than a singlet. According to molecular orbital theory, the electron configuration of triplet oxygen has two electrons occupying two π molecular orbitals (MOs) of equal energy (that is, degenerate MOs). In accordance with Hund's rules, they remain unpaired and spin parallel, which accounts for the paramagnetism of molecular oxygen. These half filled orbitals are antibonding in character, reducing the overall bond order of the molecule to 2 from the maximum value of 3 that would occur when these antibonding orbitals remain fully unoccupied, as in dinitrogen. The molecular term symbol for triplet oxygen is 3Σ. Spin
The s = spins of the two electrons in degenerate orbitals gives rise to 2 × 2 = 4 independent spin states in total. Exchange interaction splits these into a singlet state (total spin S = 0) and a set of 3 degenerate triplet states (S = 1). In agreement with Hund's rules, the triplet states are energetically more favorable, and correspond to the ground state of the molecule with a total electron spin of S = 1. Excitation to the S = 0 state results in much more reactive, metastable singlet oxygen. Lewis structure
Because the molecule in its ground state has a non zero spin magnetic moment, oxygen is paramagnetic; i. e., it can be attracted to the poles of a magnet. Thus, the Lewis structure O=O with all electrons in pairs does not accurately represent the nature of the bonding in molecular oxygen. However, the alternative structure •O–O• is also inadequate, since it implies single bond character, while the experimentally determined bond length of 121 pm is much shorter than the single bond in hydrogen peroxide (HO–OH) which has a length of 147.5 pm. This indicates that triplet oxygen has a higher bond order. Molecular orbital theory must be used to correctly account for the observed paramagnetism and short bond length simultaneously. Under a molecular orbital theory framework, the oxygen oxygen bond in triplet dioxygen is better described as one full σ bond plus two π half bonds, each half bond accounted for by two center three electron (2c 3e) bonding, to give a net bond order of two (1+2×), while also accounting for the spin state (S'' = 1). In the case of triplet dioxygen, each 2c 3e bond consists of two electrons in a πu bonding orbital and one electron in a πg antibonding orbital to give a net bond order contribution of
The usual rules for constructing Lewis structures must be modified to accommodate molecules like triplet dioxygen or nitric oxide that contain 2c 3e bonds. There is no consensus in this regard; Pauling has suggested the use of three closely spaced collinear dots to represent the three electron bond (see illustration).
Спины двух электронов в вырожденных орбиталях (s = спины) приводят к 2 × 2 = 4 независимым спиновым состояниям. Обменное взаимодействие разделяет их на синглетное состояние (общий спин S = 0) и набор из 3 вырожденных триплетных состояний (S = 1). В соответствии с правилами Хунда, триплетные состояния энергетически более выгодны и соответствуют основному состоянию молекулы с общим спином электрона S = 1. Возбуждение в состояние S = 0 приводит к гораздо более реактивному, метастабильному синглетному кислороду. Структура Льюиса
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| Name =
| ImageFile = Triplet dioxygen. png
| ImageFile3 =
| OtherNames =
| IUPACName = Triplet oxygen
| SystematicName = Dioxidanediyl (substitutive)
dioxygen(2•)(triplet) it is more stable as a triplet than a singlet. According to molecular orbital theory, the electron configuration of triplet oxygen has two electrons occupying two π molecular orbitals (MOs) of equal energy (that is, degenerate MOs). In accordance with Hund's rules, they remain unpaired and spin parallel, which accounts for the paramagnetism of molecular oxygen. These half filled orbitals are antibonding in character, reducing the overall bond order of the molecule to 2 from the maximum value of 3 that would occur when these antibonding orbitals remain fully unoccupied, as in dinitrogen. The molecular term symbol for triplet oxygen is 3Σ. Spin
The s = spins of the two electrons in degenerate orbitals gives rise to 2 × 2 = 4 independent spin states in total. Exchange interaction splits these into a singlet state (total spin S = 0) and a set of 3 degenerate triplet states (S = 1). In agreement with Hund's rules, the triplet states are energetically more favorable, and correspond to the ground state of the molecule with a total electron spin of S = 1. Excitation to the S = 0 state results in much more reactive, metastable singlet oxygen. Lewis structure
Because the molecule in its ground state has a non zero spin magnetic moment, oxygen is paramagnetic; i. e., it can be attracted to the poles of a magnet. Thus, the Lewis structure O=O with all electrons in pairs does not accurately represent the nature of the bonding in molecular oxygen. However, the alternative structure •O–O• is also inadequate, since it implies single bond character, while the experimentally determined bond length of 121 pm is much shorter than the single bond in hydrogen peroxide (HO–OH) which has a length of 147.5 pm. This indicates that triplet oxygen has a higher bond order. Molecular orbital theory must be used to correctly account for the observed paramagnetism and short bond length simultaneously. Under a molecular orbital theory framework, the oxygen oxygen bond in triplet dioxygen is better described as one full σ bond plus two π half bonds, each half bond accounted for by two center three electron (2c 3e) bonding, to give a net bond order of two (1+2×), while also accounting for the spin state (S'' = 1). In the case of triplet dioxygen, each 2c 3e bond consists of two electrons in a πu bonding orbital and one electron in a πg antibonding orbital to give a net bond order contribution of
The usual rules for constructing Lewis structures must be modified to accommodate molecules like triplet dioxygen or nitric oxide that contain 2c 3e bonds. There is no consensus in this regard; Pauling has suggested the use of three closely spaced collinear dots to represent the three electron bond (see illustration).
Поскольку молекула в основном состоянии имеет ненулевой спиновый магнитный момент, кислород является парамагнитным, то есть может притягиваться к полюсам магнита. Таким образом, структура Льюиса O=O, где все электроны спарены, неточно отражает природу связи в молекулярном кислороде. Однако альтернативная структура •O–O• также неадекватна, поскольку предполагает одинарную связь, в то время как экспериментально определенная длина связи 121 пм значительно короче, чем длина одинарной связи в перекиси водорода (HO–OH), которая составляет 147,5 пм. Это указывает на то, что триплетный кислород имеет более высокий порядок связи. Для правильного объяснения наблюдаемого парамагнетизма и короткой длины связи одновременно необходимо использовать теорию молекулярных орбиталей. В рамках теории молекулярных орбиталей кислород-кислородная связь в триплетном диоксигене лучше описывается как одна полная σ-связь и две π-полусвязи, каждая из которых обусловлена двухцентровой трехэлектронной (2c 3e) связью, что дает суммарный порядок связи равный двум (1 + 2×), а также учитывает спиновое состояние (S'' = 1). В случае триплетного диоксигена каждая 2c 3e связь состоит из двух электронов в πu-связывающей орбитали и одного электрона в πg-антисвязывающей орбитали, что вносит вклад в суммарный порядок связи. Обычные правила построения структур Льюиса необходимо модифицировать для учета молекул, таких как триплетный диоксиген или оксид азота, которые содержат 2c 3e связи. В этом отношении нет единого мнения; Полинг предложил использовать три близко расположенные коллинеарные точки для представления трехэлектронной связи (см. иллюстрацию).
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| Name =
| ImageFile = Triplet dioxygen. png
| ImageFile3 =
| OtherNames =
| IUPACName = Triplet oxygen
| SystematicName = Dioxidanediyl (substitutive)
dioxygen(2•)(triplet) it is more stable as a triplet than a singlet. According to molecular orbital theory, the electron configuration of triplet oxygen has two electrons occupying two π molecular orbitals (MOs) of equal energy (that is, degenerate MOs). In accordance with Hund's rules, they remain unpaired and spin parallel, which accounts for the paramagnetism of molecular oxygen. These half filled orbitals are antibonding in character, reducing the overall bond order of the molecule to 2 from the maximum value of 3 that would occur when these antibonding orbitals remain fully unoccupied, as in dinitrogen. The molecular term symbol for triplet oxygen is 3Σ. Spin
The s = spins of the two electrons in degenerate orbitals gives rise to 2 × 2 = 4 independent spin states in total. Exchange interaction splits these into a singlet state (total spin S = 0) and a set of 3 degenerate triplet states (S = 1). In agreement with Hund's rules, the triplet states are energetically more favorable, and correspond to the ground state of the molecule with a total electron spin of S = 1. Excitation to the S = 0 state results in much more reactive, metastable singlet oxygen. Lewis structure
Because the molecule in its ground state has a non zero spin magnetic moment, oxygen is paramagnetic; i. e., it can be attracted to the poles of a magnet. Thus, the Lewis structure O=O with all electrons in pairs does not accurately represent the nature of the bonding in molecular oxygen. However, the alternative structure •O–O• is also inadequate, since it implies single bond character, while the experimentally determined bond length of 121 pm is much shorter than the single bond in hydrogen peroxide (HO–OH) which has a length of 147.5 pm. This indicates that triplet oxygen has a higher bond order. Molecular orbital theory must be used to correctly account for the observed paramagnetism and short bond length simultaneously. Under a molecular orbital theory framework, the oxygen oxygen bond in triplet dioxygen is better described as one full σ bond plus two π half bonds, each half bond accounted for by two center three electron (2c 3e) bonding, to give a net bond order of two (1+2×), while also accounting for the spin state (S'' = 1). In the case of triplet dioxygen, each 2c 3e bond consists of two electrons in a πu bonding orbital and one electron in a πg antibonding orbital to give a net bond order contribution of
The usual rules for constructing Lewis structures must be modified to accommodate molecules like triplet dioxygen or nitric oxide that contain 2c 3e bonds. There is no consensus in this regard; Pauling has suggested the use of three closely spaced collinear dots to represent the three electron bond (see illustration).
Наблюдение в жидком состоянии
Обычный экспериментальный способ наблюдения парамагнетизма диоксигена — охладить его до жидкого состояния. Если жидкий кислород налить между полюсами сильных, близко расположенных магнитов, он может зависнуть в воздухе. Или магнит может притягивать струю жидкого кислорода во время наливания. Результирующий магнитный момент, обусловленный полным спином электронов, объясняет эти наблюдения.
Реакция
Необычная электронная конфигурация препятствует прямой реакции молекулярного кислорода со многими другими молекулами, которые часто находятся в синглетном состоянии. Однако триплетный кислород легко реагирует с молекулами в дублетном состоянии, образуя новый радикал. Для сохранения спинового квантового числа в реакции триплетного кислорода с молекулой с закрытой оболочкой (находящейся в синглетном состоянии) потребовалось бы триплетное переходное состояние. Дополнительная энергия, необходимая для этого, достаточна для предотвращения прямой реакции при комнатной температуре со всеми, кроме наиболее реакционноспособных субстратов, например, с белым фосфором. При более высоких температурах или в присутствии подходящих катализаторов реакция протекает легче. Например, большинство горючих веществ характеризуются температурой самовоспламенения, при которой они воспламеняются в воздухе без внешнего пламени или искры.
Внешние источники
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