What is Hydrogen bonding: Definition and 30 Discussions

A hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative atom or group, and another electronegative atom bearing a lone pair of electrons—the hydrogen bond acceptor (Ac). Such an interacting system is generally denoted Dn–H···Ac, where the solid line denotes a polar covalent bond, and the dotted or dashed line indicates the hydrogen bond. The most frequent donor and acceptor atoms are the second-row elements nitrogen (N), oxygen (O), and fluorine (F)
Hydrogen bonds can be intermolecular (occurring between separate molecules) or intramolecular (occurring among parts of the same molecule). Depending on the nature of the donor and acceptor atoms which constitute the bond, their geometry, and environment, the energy of a hydrogen bond can vary between 1 and 40 kcal/mol. This makes them somewhat stronger than a van der Waals interaction, and weaker than fully covalent or ionic bonds. This type of bond can occur in inorganic molecules such as water and in organic molecules like DNA and proteins. Hydrogen bonds are responsible for holding such materials as paper and felted wool together, and for causing separate sheets of paper to stick together after becoming wet and subsequently drying.
The hydrogen bond is responsible for many of the anomalous physical and chemical properties of compounds of N, O, and F. In particular, intermolecular hydrogen bonding is responsible for the high boiling point of water (100 °C) compared to the other group 16 hydrides that have much weaker hydrogen bonds. Intramolecular hydrogen bonding is partly responsible for the secondary and tertiary structures of proteins and nucleic acids. It also plays an important role in the structure of polymers, both synthetic and natural.

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  1. casparov

    I Physics of paper absorbing Water -- Doesn't this decrease Entropy?

    Summary: doesn't this decrease entropy ? Cellulose is known for its hydrophilic quality, which can be explained from the polarity of its hydroxyl groups. We all know water can overcome the force of gravity through a piece of paper you put in the water. Correct me if I'm wrong but this is a...
  2. P

    Hydrogen bonding preference in acids

    I can't figure out why hydrogen is more likely to bond to either the nitrogen or to the sulphur atom. I can't locate any information in any textbooks or online as to which molecule is more prevalent/common. This is not a homework question. I just came across one of these molecules and wondered...
  3. P

    Hydrogen bonding in human skin

    if the human skin consists of hydrogen, then why does not happen hydrogen bond through contact with something or with another person?
  4. Z

    Methyl 2 hydroxybenzoate hydrogen bonding

    Homework Statement How many hydrogen bonds can methyl 2-hydroxybenzoate form with molecules of the same compind? Homework Equations N/A The Attempt at a Solution There's a hydroxyl group on the second carbon of the benzene ring and a double-bonded oxygen with 2(3?) lone pairs, so I'm...
  5. ScepticAmatuer

    Boiling point of water heated via microwave

    I took about 100 ml of distilled water, put a small, clean rock in it (to prevent "bumping" or explosion) and heated it repeatedly in a microwave oven on high for 45 seconds. After each heating I checked the temperature of the water with a digital temperature probe. I did this 7 or 8 times...
  6. Priyadarshini

    Van der Waals' Forces and Hydrogen Bonding

    Induced dipoles result in Van der Waals' forces and permanent dipoles in hydrogen bonds, right? But how do you know is a compound has formed hydrogen bonds or Van der Waals' forces? For example, HF forms hydrogen bonds while HCl forms Van der Waals' forces and not hydrogen bonds. But in HCl, H...
  7. S

    Hydrogen bonding in Cytosine and Guanine

    Homework Statement The problem was to tell how many hydrogen bonds there are between cytosine and guanine. and I know there are three. http://study.com/cimages/multimages/16/Cytosine_Guanine_base_pair.png But I think I might be misunderstanding the hydrogen bond concept. I thought that hydrogen...
  8. gracy

    Effect of intermolecular hydrogen bonding

    Effect of intermolecular hydrogen bonding is as follows I don't understand one point i.e how occurrence of liquid state is associated with intermolecular hydrogen bonding as intermolecular hydrogen bonding helps in closed packing of molecules it should give rise to solid state.
  9. S

    Hydrogen bonding force problem

    Homework Statement In a DNA molecule, the base pair adenine and thymine is held together by two hydrogen bonds (see figure below). Let's model one of these hydrogen bonds as four point charges arranged along a straight line. Using the information in the figure below, calculate the...
  10. P

    What Units are Used for Hansen Solubility Parameter?

    For those of you who know what a Hansen Solubility Parameter is, does the "hydrogen-bonding" part means the actual hydrogen bond energy between molecules? I'm confused as to why they used mPa^0.5 instead of kJ/mol^-1 for measurement.
  11. P

    Does acidity and hydrogen bond strength go hand in hand?

    More acidity means more electronegativity, and more electronegativity means more dipole moments. I observed that liquids with low dipole moments (bases) often have lower density and surface tension, but not necessarily hydrogen bonds. To contradict it, acetic acid have a low surface tension but...
  12. P

    Hydrogen Bond Strength: Strengthen & Weaken in Water

    How do you strengthen and weaken hydrogen bonds in water aside from changing its temperature? Could you add any solutes to do so?
  13. D

    Why isn't the ion NH4+ capable of hydrogen bonding?

    If you draw lewis structure, central atom (N) will have 1 lone pair and 4 single bonds with Hydrogen. Why can't hydrogen in this ion molecule be able to form hydrogen bonding with other molecules alike? Is it because there's only 1 electron on the central atom?See for yourself: 5N + 4H -1 = 9...
  14. D

    Chemistry Why does Hexane have higher intermolecular force than Propylamine?

    < Moderator Note -- thread moved to Homework Help forums > Shouldn't Propylamine (C3H7NH2) be able to form hydrogen bonds with alike molecules? Hexane (c6h14) doesn't seem to have hydrogen bonding capability.
  15. S

    What causes differences in polarity between alcohol and ketone molecules?

    What is the relationship between polarity and hydrogen bonding? I have come across several problems saying that an alcohol is more polar than a ketone because of hydrogen bonding but I don't see the relationship between these two. Intuitively, I thought ketone would be more polar because it has...
  16. Jadaav

    Intermolecular and intramolecular hydrogen bonding

    Intermolecular hydrogen bonding is stronger than intramolecular hydrogen bonding. But how to differentiate between an intermolecular and an intramolecular hydrogen bonding ? How can I know if there is the presence of an intermolecular or an intramolecular hydrogen bonding in a molecule ?
  17. P

    Understanding Hydrogen Bonding in Ethanol Molecules

    Hey, How do you know how many hydrogen bonds ethanol molecules will form with each other? I know there are 3 sites where H bonds could form (2 lone pairs on oxygen and the hydrogen) but with something like hydrogen fluoride, each molecule only forms 1 H bond on average so shouldn't something...
  18. P

    Chemistry Hydrogen bonding between water and other molecules.

    Homework Statement I have attached a solution to one of my homework questions that states "Draw hydrogen bonds that might be formed between a water molecule and the following compounds: a) H3PO4; b) PO43-; c) aniline; d) pyridine; e) ethylamine; f) ethyl ammonium ion; g) acetic acid." My...
  19. M

    Chlorine and Hydrogen Bonding: Examining the Strength and Nature of Interactions

    Does chlorine make a hydrogen bond? I was doing a practice problem in my book and the question was regarding the intermolecular forces, and the compound had chlorine and it said no, but my professor said it does. Which is true?
  20. B

    Is Significant Hydrogen Bonding Possible in Phosphine (PH3)?

    Homework Statement is significant hydorgen bonding possible in phosphine, PH3 The Attempt at a Solution The text says no, I don't see why not. P has 5 electrons in its outer shells, 3 of those form an ionic bond with the 3 H. That leaves 2 non-binding electrons, those 2 non-binding...
  21. B

    Which substance exhibits the most hydrogen bonding?

    Homework Statement Which of the following substances exhibits significant hydrogen bonding in the liquid state? A) CH_{2}F_{2} B) N_{2}H_{4} C) CH_{3}OCH_{3} D) C_{2}H_{4} E) C_{2}H_{2} Homework Equations The Attempt at a Solution I know that hydrogen bonding generally only works...
  22. K

    Hydrogen bonding and Oxygen electron count ? (how)

    Sorry to butt in on your form. Please can someone help me with this – I’m sure it’s simple to those who know but I have been thinking about these 2 problems for ages (and reading up on every website I can find) and still no answer. I am trying to get a basic understanding of this and seem to...
  23. G

    Understanding Hydrogen Bonding in Water and Fluorine: A Comparison

    Every water molecule is H-bonded with up to four other molecules (two through its two lone pairs, and two through its two hydrogen atoms. These 4 intermolecular hydrogen bonds are what contribute to water's high boiling point.. My textbook compares this with Fluorine, which it says can...
  24. V

    The Double Helix - Hydrogen bonding and stability

    Rank the following base pairs according to their stability. Rank from most to least stable. To rank items as equivalent, overlap them. ------------- I have found out that the first one is thymine-adenine pair and the second one is a cytosine-guanine pair. The third one is cytosine...
  25. S

    Anyone aware of the Physics of Hydrogen Bonding ? Please suggest resources

    Anyone aware of the Physics of Hydrogen Bonding ?? Please suggest resources ! Hi everyone, Am a grad student doing experimental research in an interdisciplinary lab of nanoscience - I am using the concept of hydrogen bonding in some of my experiments. I am planning to...
  26. M

    Illustrate Hydrogen Bonding: Amino Acids

    Homework Statement The following structures illustrate hydrogen bonding interactions between amino acid side chains and/or backbone atoms within a protein structure. In which of the following figures are the structures and hydrogen bonding completely correct? Homework Equations...
  27. P

    Hydrogen bonding with NH3 .help.

    hydrogen bonding with NH3 please.help.ASAP! Homework Statement NH3 is a donor & acceptor of hydrogen in hydrogen bond formation...Draw a diagram to show the H bonding of an ammonia molecule w/2 other NH3 molecule. Homework Equations The Attempt at a Solution this is waht i...
  28. H

    Types of Bonding in CH3CHO: A Is the Answer

    [SOLVED] Hydrogen bonding Which types of bonding are present in CH3CHO(=ethanal) in the liquid state? I. Single covalent bonding II. Double covalent bonding III. Hydrogen bonding A. I and II only B. I and III only C. II and III only D. I, II and III The solution is A but I can not...
  29. C

    Hydrogen bonding. Why isn't Cl included?

    I was wondering why hydrogen bonding only occurs in molecules containing H and one or more of the following: N, O, and F. Why isn't Cl included in this list? The reason I ask is because the electronegativity of Cl is very close to (and even equal to one of) the electronegativities of the...
  30. S

    Separate Ethanol from Water: Hydrogen Bonding

    Hi, i have more of a chemistry than a physics question. I am conducting an experiment to separate ethanol from water via fractional distillation, however through calculations i have found that some of the ethanol remains bonded to the water due to the strong hydrogen bonds. Is there any other...