A
hydrogen bond is the attractive interaction of a
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
atom with an electronegative atom, like
nitrogenNitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere.Many industrially important...
,
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
or
fluorineFluorine is the chemical element with atomic number 9, represented by the symbol F. Fluorine forms a single bond with itself in elemental form, resulting in the diatomic F
2 molecule. F
2 is a supremely reactive, poisonous, pale, yellowish brown gas. Elemental fluorine is the...
(thus the name "hydrogen bond", which must not be confused with a
covalent bondA covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds...
to hydrogen). The hydrogen must be covalently bonded to another electronegative atom to create the bond. These bonds can occur between molecules (
intermolecularly), or within different parts of a single molecule (
intramolecularly). The hydrogen bond (5 to 30 kJ/mole) is stronger than a
van der Waals interactionIn physical chemistry, the van der Waals force , named after Dutch scientist Johannes Diderik van der Waals, is the attractive or repulsive force between molecules other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral molecules...
, but weaker than
covalentA covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds...
or
ionic bondAn ionic bond is a type of chemical bond that involves a metal and a nonmetal ion through electrostatic attraction. In short, it is a bond formed by the attraction between two oppositely charged ions....
s. This type of bond occurs in both inorganic molecules such as water and organic molecules such as DNA.
Intermolecular hydrogen bonding is responsible for the high boiling point of
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
(100 °C). This is because of the strong hydrogen bond, as opposed to other
group 16The chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family...
hydrideHydride is the name given to the negative ion of hydrogen, H−. Practically, the term hydride has two distinct but overlapping meanings. In the chemical vernacular the term hydride refers to a hydrogen atom that formally reacts as a hydrogen anion under common conditions as well as...
s. Intramolecular hydrogen bonding is partly responsible for the
secondaryIn biochemistry and structural biology, secondary structure is the general three-dimensional form of local segments of biopolymers such as proteins and nucleic acids...
,
tertiaryIn biochemistry and chemistry, the tertiary structure of a protein or any other macromolecule is its three-dimensional structure, as defined by the atomic coordinates.-Relationship to primary structure:...
, and
quaternary structureIn biochemistry, quaternary structure is the arrangement of multiple folded protein molecules in a multi-subunit complex.-Description and examples:...
s of
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
s and
nucleic acidA nucleic acid is a macromolecule composed of chains of monomeric nucleotides. In biochemistry these molecules carry genetic information or form structures within cells. The most common nucleic acids are deoxyribonucleic acid and ribonucleic acid . Nucleic acids are universal in living things, as...
s.
Bonding
A hydrogen atom attached to a relatively
electronegativeElectronegativity, symbol χ, is a chemical property that describes the ability of an atom to attract electrons towards itself in a covalent bond. An atom's electronegativity is affected by both its atomic weight and the distance that its valence electrons reside from the charged nucleus...
atom is a hydrogen bond donor. This electronegative atom is usually
fluorineFluorine is the chemical element with atomic number 9, represented by the symbol F. Fluorine forms a single bond with itself in elemental form, resulting in the diatomic F
2 molecule. F
2 is a supremely reactive, poisonous, pale, yellowish brown gas. Elemental fluorine is the...
,
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
, or
nitrogenNitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere.Many industrially important...
. An electronegative atom such as fluorine, oxygen, or nitrogen is a hydrogen bond acceptor, regardless of whether it is bonded to a hydrogen atom or not. An example of a hydrogen bond donor is
ethanolEthanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug, best known as the type of alcohol found in alcoholic beverages and in modern thermometers. Ethanol is one of the oldest recreational drugs...
, which has a hydrogen bonded to oxygen; an example of a hydrogen bond acceptor which
does not have a hydrogen atom bonded to it is the oxygen atom on
diethyl etherDiethyl ether, also known as ether, ethyl ether and ethoxyethane, is a clear, colorless, and highly flammable liquid with a low boiling point and a characteristic odor. It is the most common member of a class of chemical compounds known generically as ethers. It is an isomer of butanol...
.
A hydrogen attached to
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
can also participate in hydrogen bonding when the carbon atom is bound to electronegative atoms, as is the case in
chloroformChloroform is the organic compound with formula CHCl
3. This colourless, sweet-smelling, dense liquid is a trihalomethane. It is also considered somewhat hazardous...
, CHCl
3. The electronegative atom attracts the electron cloud from around the hydrogen nucleus and, by decentralizing the cloud, leaves the atom with a positive partial charge. Because of the small size of hydrogen relative to other atoms and molecules, the resulting charge, though only partial, nevertheless represents a large charge density. A hydrogen bond results when this strong positive charge density attracts a
lone pairA lone pair is a electron pair without bonding or sharing with other atoms. They are found in the outermost electron shell of an atom, so lone pairs are a subset of a molecule's valence electrons...
of electrons on another
heteroatomIn the nomenclature of organic chemistry, a heteroatom is any atom that is not carbon or hydrogen...
, which becomes the hydrogen-bond
acceptor.
The hydrogen bond is often described as an electrostatic dipole-dipole interaction. However, it also has some features of covalent bonding: it is directional, strong, produces interatomic distances shorter than sum of van der Waals radii, and usually involves a limited number of interaction partners, which can be interpreted as a kind of
valenceIn chemistry, valence, also known as valency or valency number, is a measure of the number of chemical bonds formed by the atoms of a given element...
. These covalent features are more significant when acceptors bind hydrogens from more electronegative donors.
The partially covalent nature of a hydrogen bond raises the questions: "To which molecule or atom does the hydrogen
nucleusThe nucleus is the very dense region consisting of nucleons at the center of an atom. Almost all of the mass in an atom is made up from the protons and neutrons in the nucleus, with a very small contribution from the orbiting electrons....
belong?" and "Which should be labeled 'donor' and which 'acceptor'?" Usually, this is easy to determine simply based on interatomic distances in the X—H
...Y system: X—H distance is typically ~110
pmA picometre is a unit of length in the metric system, equal to one trillionth or one billionth , i.e. of a meter, which is the current SI base unit of length...
, whereas H
...Y distance is ~160 to 200 pm. Liquids that display hydrogen bonding are called
associated liquids.
Hydrogen bonds can vary in strength from very weak (1-2 kJ mol
−1) to extremely strong (>155 kJ mol
−1), as in the ion ]]. Typical values include:
- F—H...:F (155 kJ/mol or 40 kcal/mol)
- O—H...:N (29 kJ/mol or 6.9 kcal/mol)
- O—H...:O (21 kJ/mol or 5.0 kcal/mol)
- N—H...:N (13 kJ/mol or 3.1 kcal/mol)
- N—H...:O (8 kJ/mol or 1.9 kcal/mol)
- HO—H...: (18 kJ/mol or 4.3 kcal/mol) {Data obtained using molecular dynamics
Molecular dynamics is a form of computer simulation in which atoms and molecules are allowed to interact for a period of time by approximations of known physics,...
as detailed in the reference and should be compared to 7.9 kJ/mol for bulk waters, obtained using the same molecular dynamicsMolecular dynamics is a form of computer simulation in which atoms and molecules are allowed to interact for a period of time by approximations of known physics,...
.}
The length of hydrogen bonds depends on bond strength, temperature, and pressure. The bond strength itself is dependent on temperature, pressure, bond angle, and environment (usually characterized by local
dielectricA dielectric is a nonconducting substance, i.e. an insulator. The term was coined by William Whewell in response to a request from Michael Faraday...
constant). The typical length of a hydrogen bond in water is 197 pm. The ideal bond angle depends on the nature of the hydrogen bond donor. Experimental results of hydrofluoric acid donor with various acceptors shows the following angles:
| Acceptor···Donor |
VSEPR Symmetry |
Angle (°) |
| HCN···HF |
linear |
180 |
| H2CO ··· HF |
trigonal planar |
110 |
| H2O ··· HF |
pyramidal |
46 |
| H2S ··· HF |
pyramidal |
89 |
| SO2 ··· HF |
trigonal |
145 |
History
In his book
The Nature of the Chemical Bond, Linus Pauling credits T.S. Moore and T.F. Winmill with the first mention of the hydrogen bond, in 1912 (J. Chem. Soc. 101, 1635). Moore and Winmill used the hydrogen bond to account for the fact that trimethylammonium hydroxide is a weaker base than
tetramethylammonium hydroxideTetramethylammonium hydroxide is a quaternary ammonium salt with the molecular formula
4NOH. It is used as an anisotropic etchant of silicon. It is also used as a basic solvent in the development of acidic photoresist in the photolithography process. Since it is a phase transfer...
. The description of hydrogen bonding in its more well-known setting, water, came some years later, in 1920, from Latimer and Rodebush (JACS, 42, 1419). In that paper, Latimer and Rodebush cite work by a fellow scientist at the laboratory,
Maurice Loyal HugginsMaurice Loyal Huggins was a scientist who independently conceived the idea of hydrogen bonding and who was an early advocate for their role in stabilizing protein secondary structure...
, saying, "Mr. Huggins of this laboratory in some work as yet unpublished, has used the idea of a hydrogen kernel held between two atoms as a theory in regard to certain organic compounds."
Hydrogen bonds in water
The most ubiquitous, and perhaps simplest, example of a hydrogen bond is
found between
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
molecules. In a discrete water molecule, water has two hydrogen atoms and one oxygen atom. Two molecules of
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
can form a hydrogen bond between them; the simplest case, when only two molecules are present, is called the
water dimerThe water dimer consists of two water molecules loosely bound by a hydrogen bond. It is the smallest water cluster. Because it is the simplest model system for studying hydrogen bonding in water, it has been the target of so many theoretical studies that it has been called "a theoretical Guinea...
and is often used as a model system. When more molecules are present, as is the case in liquid water, more bonds are possible because the oxygen of one water molecule has two lone pairs of electrons, each of which can form a hydrogen bond with a hydrogen on another water molecule. This can repeat so that every water molecule is H-bonded with up to four other molecules, as shown in the figure (two through its two lone pairs, and two through its two hydrogen atoms).
LiquidLiquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material. The surface is a free surface where the liquid is not constrained by a container....
water's high
boiling pointThe boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....
is due to the high number of hydrogen bonds each molecule can have relative to its low
molecular massThe molecular mass of a substance, frequently referred to by the older term molecular weight and abbreviated as MW, is the mass of one molecule of that substance, relative to the unified atomic mass unit u...
. Due to the difficulty of breaking these bonds, water has a very high boiling point, melting point, and viscosity compared to other similar liquids not conjoined by hydrogen bonds. Water is unique because its oxygen atom has two lone pairs and two hydrogen atoms, meaning that the total number of bonds of a water molecule is up to four. For example, hydrogen fluoride—which has three lone pairs on the F atom but only one H atom—can have a total of only two bonds (
ammoniaAmmonia is a compound of nitrogen and hydrogen with the formula NH
3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers...
has the opposite problem: three hydrogen atoms but only one lone pair).
- H-F...H-F...H-F
The exact number of hydrogen bonds in which a molecule in liquid water participates, fluctuates with time and depends on the temperature. From
TIP4PIn computational chemistry, classical water models are used for the simulation of water clusters, liquid water, and aqueous solutions with explicit solvent. These models use the approximations of molecular mechanics...
liquid water simulations at 25 °C, it was estimated that each water molecule participates in an average of 3.59 hydrogen bonds. At 100 °C, this number decreases to 3.24 due to the increased molecular motion and decreased density, while at 0 °C, the average number of hydrogen bonds increases to 3.69. A more recent study found a much smaller number of hydrogen bonds: 2.357 at 25 °C. The differences may be due to the use of a different method for defining and counting the hydrogen bonds.
Where the bond strengths are more equivalent, one might instead find the atoms of two interacting water molecules partitioned into two
polyatomic ionA polyatomic ion, also known as a molecular ion, is a charged species composed of two or more atoms covalently bonded or of a metal complex that can be considered as acting as a single unit in the context of acid and base chemistry or in the formation of salts. The prefix poly- means many in...
s of opposite charge, specifically
hydroxideIn chemistry, hydroxide is the name for the diatomic anion OH−, consisting of oxygen and hydrogen atoms, usually derived from the dissociation of a base. It is one of the simplest diatomic ions known....
(OH
−) and
hydroniumIn chemistry, hydronium is the common name for the aqueous cation , the simplest type of oxonium ion, produced by protonation of water. It is the positive ion present when an Arrhenius acid is dissolved in water, as Arrhenius acid molecules in solution give up a proton to the surrounding water...
(H
3O
+). (Hydronium ions are also known as 'hydroxonium' ions.)
- H-O− H3O+
Indeed, in pure water under conditions of standard temperature and pressure, this latter formulation is applicable only rarely; on average about one in every 5.5 × 10
8 molecules gives up a proton to another water molecule, in accordance with the value of the
dissociation constantIn chemistry, biochemistry, and pharmacology, a dissociation constant is a specific type of equilibrium constant that measures the propensity of a larger object to separate reversibly into smaller components, as when a complex falls apart into its component molecules, or when a salt splits up into...
for water under such conditions. It is a crucial part of the uniqueness of water.
Bifurcated and over-coordinated hydrogen bonds in water
It can be that a single hydrogen atom participates in two hydrogen bonds, rather than one. This type of bonding is called "bifurcated".It can exist for instance in complex natural or synthetic organic molecules It was suggested that a bifurcated hydrogen atom is an essential step in water reorientation;.
Acceptor type hydrogen bonds (terminating on an oxygens` lone pairs), are more likely to form bifurcation (in fact, it is called over coordinated oxygen, OCO) than donor type, beginning on the same oxygens` hydrogens .
Hydrogen bonds in DNA and proteins
Hydrogen bonding also plays an important role in determining the three-dimensional structures adopted by proteins and nucleic bases. In these macromolecules, bonding between parts of the same macromolecule cause it to fold into a specific shape, which helps determine the molecule's physiological or biochemical role. The double helical structure of
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
, for example, is due largely to hydrogen bonding between the
base pairIn molecular biology, two nucleotides on opposite complementary DNA or RNA strands that are connected via hydrogen bonds are called a base pair . In the canonical Watson-Crick base pairing, adenine forms a base pair with thymine , as does guanine with cytosine in DNA. In RNA, thymine is replaced...
s, which link one complementary strand to the other and enable
replicationDNA replication, the basis for biological inheritance, is a fundamental process occurring in all living organisms to copy their DNA. This process is "semiconservative" in that each strand of the original double-stranded DNA molecule serves as template for the reproduction of the complementary strand...
.
In the secondary structure of proteins, hydrogen bonds form between the backbone oxygens and amide hydrogens. When the spacing of the
amino acidAmino acids are molecules containing an amine group, a carboxylic acid group and one of the twenty R-groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H
2NCHRCOOH, where R is an organic substituent...
residues participating in a hydrogen bond occurs regularly between positions
i and
i + 4, an
alpha helixA common motif in the secondary structure of proteins, the alpha helix is a right- or left-handed coiled conformation, resembling a spring, in which every backbone N-H group donates a hydrogen bond to the backbone C=O group of the amino acid four residues earlier...
is formed. When the spacing is less, between positions
i and
i + 3, then a
310 helixA 3
10 helix is a type of secondary structure found in proteins.-Structure:The amino acids in a 3
10-helix are arranged in a right-handed helical structure. Each amino acid corresponds to a 120° turn in the helix , and a translation of 2.0 Å along the helical axis...
is formed. When two strands are joined by hydrogen bonds involving alternating residues on each participating strand, a
beta sheetThe β sheet is the second form of regular secondary structure in proteins consisting of beta strands connected laterally by five or more hydrogen bonds, forming a generally twisted, pleated sheet...
is formed. Hydrogen bonds also play a part in forming the tertiary structure of protein through interaction of R-groups. (See also
protein foldingProtein folding is the physical process by which a polypeptide folds into its characteristic and functional three-dimensional structure from random coil....
).
Symmetric hydrogen bond
A symmetric hydrogen bond is a special type of hydrogen bond in which the proton is spaced exactly halfway between two identical atoms. The strength of the bond to each of those atoms is equal. It is an example of a 3-center 4-electron bond. This type of bond is much stronger than "normal" hydrogen bonds. The effective bond order is 0.5, so its strength is comparable to a covalent bond. It is seen in ice at high pressure, and also in the solid phase of many anhydrous acids such as hydrofluoric acid and formic acid at high pressure. It is also seen in the bifluoride ion [F-H-F]
−.
Symmetric hydrogen bonds have been observed recently spectroscopically in
formic acidFormic acid is the simplest carboxylic acid. Its formula is HCOOH or CH2O2. It is an important intermediate in chemical synthesis and occurs naturally, most notably in the venom of bee and ant stings.In nature, it is found in the stings and bites of many insects of the order...
at high pressure (>GPa). Each hydrogen atom forms a partial covalent bond with two atoms rather than one. Symmetric hydrogen bonds have been postulated in ice at high pressure (
Ice XIce X is a cubic crystalline form of ice formed in the same manner as ice VII, but at pressures as high as about 70 GPa. It is proton-ordered and symmetric....
).
Low-barrier hydrogen bondA Low-barrier hydrogen bond or LBHB is a special type of hydrogen bond. This type of bond is especially strong because the distance between acceptor and donor is especially short. In regular hydrogen bonds the hydrogen ion clearly belongs to one of the heteroatoms...
s form when the distance between two heteroatoms is very small.
Dihydrogen bond
The hydrogen bond can be compared with the closely related
dihydrogen bondIn chemistry, a dihydrogen bond is a kind of hydrogen bond, an interaction between a metal hydride bond and an OH or NH group or another proton donor. The first example of this phenomenon is credited to Brown and Heseltine. They observed intense absorptions in the IR bands at 3300 and...
, which is also an
intermolecularIn physics, chemistry, and biology, intermolecular forces are forces that act between stable molecules or between functional groups of macromolecules....
bonding interaction involving hydrogen atoms. These structures have been known for some time, and well characterized by
crystallographyX-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and diffracts into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a three-dimensional picture...
; however, an understanding of their relationship to the conventional hydrogen bond,
ionic bondAn ionic bond is a type of chemical bond that involves a metal and a nonmetal ion through electrostatic attraction. In short, it is a bond formed by the attraction between two oppositely charged ions....
, and
covalent bondA covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds...
remains unclear. Generally, the hydrogen bond is characterized by a proton acceptor that is a lone pair of electrons in nonmetallic atoms (most notably in the
nitrogenThe Nitrogen group is Group 15 of the periodic table and is also collectively named the pnictogens...
, and
chalcogenThe chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family...
groups). In some cases, these proton acceptors may be pi-bonds or metal complexes. In the dihydrogen bond, however, a metal hydride serves as a proton acceptor; thus forming a hydrogen-hydrogen interaction.
Neutron diffractionNeutron diffraction is a method for the determination of the atomic and/or magnetic structure of a material. It can be equally well applied to study crystalline solids , gasses, liquids or amorphous materials. Neutron diffraction is a form of elastic scattering where the neutrons exiting the...
has shown that the
molecular geometryMolecular geometry or molecular structure is the three-dimensional arrangement of the atoms that constitute a molecule. It determines several properties of a substance including its reactivity, polarity, phase of matter, color, magnetism, and biological activity.- Molecular geometry determination...
of these complexes is similar to hydrogen bonds, in that the bond length is very adaptable to the metal complex/hydrogen donor system.
Advanced theory of the hydrogen bond
Recently the nature of the bond was elucidated. A widely publicized article proved from interpretations of the
anisotropiesAnisotropy is the property of being directionally dependent, as opposed to isotropy, which implies homogeneity in all directions. It can be defined as a difference, when measured along different axes, in a material's physical property An example of anisotropy is the light coming through a...
in the
Compton profileIn physics, Compton scattering or the Compton effect is the decrease in energy of an X-ray or gamma ray photon, when it interacts with matter. Because of the change in photon energy, it is an inelastic scattering process. Inverse Compton scattering also exists, where the photon gains energy upon...
of ordinary ice, that the hydrogen bond is partly covalent. Some NMR data on hydrogen bonds in proteins also indicate covalent bonding.
Most generally, the hydrogen bond can be viewed as a
metricIn mathematics, a metric or distance function is a function which defines a distance between elements of a set. A set with a metric is called a metric space. A metric induces a topology on a set but not all topologies can be generated by a metric...
-dependent electrostatic
scalar fieldIn mathematics and physics, a scalar field associates a scalar value to every point in a space. The scalar may either be a mathematical number, or a physical quantity...
between two or more intermolecular bonds. This is slightly different from the
intramolecularIntramolecular in chemistry describes a process or characteristic limited within the structure of a single molecule; a property or phenomenon limited to the extent of a single molecule.- Examples :...
bound states of, for example,
covalentA covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds...
or
ionic bondAn ionic bond is a type of chemical bond that involves a metal and a nonmetal ion through electrostatic attraction. In short, it is a bond formed by the attraction between two oppositely charged ions....
s; however, hydrogen bonding is generally still a
bound stateIn physics, a bound state is a composite that behaves as a single object. In quantum mechanics , a bound state is a state in the Hilbert space that corresponds to two or more particles whose interaction energy is negative, and therefore these particles cannot be separated unless energy is...
phenomenon, since the
interaction energyIn physics, interaction energy is the contribution to the total energy that is caused by an interaction between the objects being considered.The interaction energy usually depends on the relative position of the objects...
has a net negative sum. The initial theory of hydrogen bonding proposed by
Linus PaulingLinus Carl Pauling was an American chemist, peace activist, author, and educator. He was one of the most influential chemists in history and ranks among the most important scientists in any field of the 20th century. Pauling was among the first scientists to work in the fields of quantum...
suggested that the hydrogen bonds had a partial covalent nature. This remained a controversial conclusion until the late 1990s when
NMR techniquesNuclear magnetic resonance is a property that magnetic nuclei have in a magnetic field and applied electromagnetic pulse, which cause the nuclei to absorb energy from the EM pulse and radiate this energy back out...
were employed by F. Cordier
et al. to transfer information between hydrogen-bonded nuclei, a feat that would only be possible if the hydrogen bond contained some covalent character. While a lot of experimental data has been recovered for hydrogen bonds in water, for example, that provide good resolution on the scale of intermolecular distances and
molecular thermodynamicsIn physics, thermodynamics is the study of the conversion of energy into work and heat and its relation to macroscopic variables such as temperature, volume and pressure...
, the
kineticKinetic theory is the theory that gases are made up of a large number of small particles , all of which are in constant, random motion. The rapidly moving particles constantly collide with each other and with the walls of the container...
and dynamical properties of the hydrogen bond in
dynamicIn physics the term dynamics customarily refers to the time evolution of physical processes. These processes may be microscopic as in particle physics, kinetic theory, and chemical reactions, or macroscopic as in the predictions of statistical mechanics and nonequilibrium thermodynamics....
systems remains unchanged.
Hydrogen bonding phenomena
- Dramatically higher boiling points of NH3, H2O, and HF compared to the heavier analogues PH3, H2S, and HCl.
- Viscosity of anhydrous phosphoric acid
Phosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral acid having the chemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more...
and of glycerolGlycerol is an organic compound, also commonly called glycerin or glycerine. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydrophilic hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. ...
- Dimer formation in carboxylic acid
Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the formula -COH, usually written -COOH or -CO2H. Carboxylic acids are Brønsted-Lowry acids — they are proton donors. Salts and anions of carboxylic acids are called...
s and hexamer formation in hydrogen fluorideHydrogen fluoride is a chemical compound with the formula HF. It is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers . HF is widely used in the petrochemical...
, which occur even in the gas phase, resulting in gross deviations from the ideal gas lawThe Ideal gas law is the equation of state of a hypothetical ideal gas. It is a good approximation to the behaviour of many gases under many conditions, although it has several limitations. It was first stated by Émile Clapeyron in 1834 as a combination of Boyle's law and Charles's law...
.
- High water solubility of many compounds such as ammonia is explained by hydrogen bonding with water molecules.
- Negative azeotropy
An azeotrope is a mixture of two or more liquids in such a ratio that its composition cannot be changed by simple distillation...
of mixtures of HF and water
- Deliquescence of NaOH is caused in part by reaction of OH- with moisture to form hydrogen-bonded species. An analogous process happens between NaNH2 and NH3, and between NaF and HF.
- The fact that ice is less dense than liquid water is due to a crystal structure stabilized by hydrogen bonds.
- The presence of hydrogen bonds can cause an anomaly in the normal succession of states of matter for certain mixtures of chemical compounds as temperature increases or decreases. These compounds can be liquid until a certain temperature, then solid even as the temperature increases, and finally liquid again as the temperature rises over the "anomaly interval"
- Smart rubber
Smart rubber is a polymer that is able to "heal" when torn.The edges of a tear can be held together, and they will simply re-bond into apparent solidity.-How it works:...
utilizes hydrogen bonding as its sole means of bonding, so that it can "heal" when torn, because hydrogen bonding can occur on the fly between two surfaces of the same polymer.
External links
- The Bubble Wall (Audio slideshow from the National High Magnetic Field Laboratory explaining cohesion, surface tension and hydrogen bonds)