Ethyl methyl ether has a structure similar to H2O; it contains two polar CO single bonds oriented at about a 109 angle to each other, in addition to relatively nonpolar CH bonds. second molecules in Group 14 is . Asked for: formation of hydrogen bonds and structure. GeCl4 (87C) > SiCl4 (57.6C) > GeH4 (88.5C) > SiH4 (111.8C) > CH4 (161C). Methane and its heavier congeners in group 14 form a series whose boiling points increase smoothly with increasing molar mass. Intermolecular forces are electrostatic in nature and include van der Waals forces and hydrogen bonds. On average, however, the attractive interactions dominate. The expansion of water when freezing also explains why automobile or boat engines must be protected by antifreeze and why unprotected pipes in houses break if they are allowed to freeze. The hydrogen atom is then left with a partial positive charge, creating a dipole-dipole attraction between the hydrogen atom bonded to the donor, and the lone electron pair on the accepton. dimethyl sulfoxide (boiling point = 189.9C) > ethyl methyl sulfide (boiling point = 67C) > 2-methylbutane (boiling point = 27.8C) > carbon tetrafluoride (boiling point = 128C). The net effect is that the first atom causes the temporary formation of a dipole, called an induced dipole, in the second. This occurs when two functional groups of a molecule can form hydrogen bonds with each other. Figure 10.2. is due to the additional hydrogen bonding. intermolecular forces in butane and along the whole length of the molecule. Each water molecule accepts two hydrogen bonds from two other water molecules and donates two hydrogen atoms to form hydrogen bonds with two more water molecules, producing an open, cagelike structure. We see that H2O, HF, and NH3 each have higher boiling points than the same compound formed between hydrogen and the next element moving down its respective group, indicating that the former have greater intermolecular forces. Intermolecular hydrogen bonds occur between separate molecules in a substance. Why do strong intermolecular forces produce such anomalously high boiling points and other unusual properties, such as high enthalpies of vaporization and high melting points? Intermolecular forces hold multiple molecules together and determine many of a substance's properties. 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Electrostatic interactions are strongest for an ionic compound, so we expect NaCl to have the highest boiling point. (see Interactions Between Molecules With Permanent Dipoles). Draw the hydrogen-bonded structures. Thus a substance such as \(\ce{HCl}\), which is partially held together by dipoledipole interactions, is a gas at room temperature and 1 atm pressure, whereas \(\ce{NaCl}\), which is held together by interionic interactions, is a high-melting-point solid. In fact, the ice forms a protective surface layer that insulates the rest of the water, allowing fish and other organisms to survive in the lower levels of a frozen lake or sea. Legal. This lesson discusses the intermolecular forces of C1 through C8 hydrocarbons. Arrange n-butane, propane, 2-methylpropane [isobutene, (CH3)2CHCH3], and n-pentane in order of increasing boiling points. Both propane and butane can be compressed to form a liquid at room temperature. These attractive interactions are weak and fall off rapidly with increasing distance. Considering CH3OH, C2H6, Xe, and (CH3)3N, which can form hydrogen bonds with themselves? These forces are generally stronger with increasing molecular mass, so propane should have the lowest boiling point and n -pentane should have the highest, with the two butane isomers falling in between. In order for a hydrogen bond to occur there must be both a hydrogen donor and an acceptor present. H2S, which doesn't form hydrogen bonds, is a gas. The cohesion-adhesion theory of transport in vascular plants uses hydrogen bonding to explain many key components of water movement through the plant's xylem and other vessels. Arrange GeH4, SiCl4, SiH4, CH4, and GeCl4 in order of decreasing boiling points. To predict the relative boiling points of the other compounds, we must consider their polarity (for dipoledipole interactions), their ability to form hydrogen bonds, and their molar mass (for London dispersion forces). Accessibility StatementFor more information contact us atinfo@libretexts.orgor check out our status page at https://status.libretexts.org. A molecule will have a higher boiling point if it has stronger intermolecular forces. Neopentane is almost spherical, with a small surface area for intermolecular interactions, whereas n-pentane has an extended conformation that enables it to come into close contact with other n-pentane molecules. Hydrogen bonding is the strongest because of the polar ether molecule dissolves in polar solvent i.e., water. GeCl4 (87C) > SiCl4 (57.6C) > GeH4 (88.5C) > SiH4 (111.8C) > CH4 (161C). Considering CH3OH, C2H6, Xe, and (CH3)3N, which can form hydrogen bonds with themselves? The three major types of intermolecular interactions are dipoledipole interactions, London dispersion forces (these two are often referred to collectively as van der Waals forces), and hydrogen bonds. The four compounds are alkanes and nonpolar, so London dispersion forces are the only important intermolecular forces. As a result, it is relatively easy to temporarily deform the electron distribution to generate an instantaneous or induced dipole. Intermolecular forces determine bulk properties such as the melting points of solids and the boiling points of liquids. Identify the most significant intermolecular force in each substance. Hydrogen bond formation requires both a hydrogen bond donor and a hydrogen bond acceptor. Examples range from simple molecules like CH3NH2 (methylamine) to large molecules like proteins and DNA. London dispersion forces are due to the formation of instantaneous dipole moments in polar or nonpolar molecules as a result of short-lived fluctuations of electron charge distribution, which in turn cause the temporary formation of an induced dipole in adjacent molecules. Comparing the two alcohols (containing -OH groups), both boiling points are high because of the additional hydrogen bonding due to the hydrogen attached directly to the oxygen - but they are not the same. The same effect that is seen on boiling point as a result of hydrogen bonding can also be observed in the viscosity of certain substances. Why do strong intermolecular forces produce such anomalously high boiling points and other unusual properties, such as high enthalpies of vaporization and high melting points? In contrast, the energy of the interaction of two dipoles is proportional to 1/r3, so doubling the distance between the dipoles decreases the strength of the interaction by 23, or 8-fold. The first two are often described collectively as van der Waals forces. They have the same number of electrons, and a similar length to the molecule. Sohail Baig Name: _ Unit 6, Lesson 7 - Intermolecular Forces (IMFs) Learning Targets: List the intermolecular forces present . (see Polarizability). Arrange 2,4-dimethylheptane, Ne, CS2, Cl2, and KBr in order of decreasing boiling points. CH3CH2Cl. Thus far we have considered only interactions between polar molecules, but other factors must be considered to explain why many nonpolar molecules, such as bromine, benzene, and hexane, are liquids at room temperature, and others, such as iodine and naphthalene, are solids. Identify the intermolecular forces present in the following solids: CH3CH2OH. Thus, the van der Waals forces are weakest in methane and strongest in butane. dimethyl sulfoxide (boiling point = 189.9C) > ethyl methyl sulfide (boiling point = 67C) > 2-methylbutane (boiling point = 27.8C) > carbon tetrafluoride (boiling point = 128C). Which of the following intermolecular forces relies on at least one molecule having a dipole moment that is temporary? Describe the types of intermolecular forces possible between atoms or molecules in condensed phases (dispersion forces, dipole-dipole attractions, and hydrogen bonding) . A Of the species listed, xenon (Xe), ethane (C2H6), and trimethylamine [(CH3)3N] do not contain a hydrogen atom attached to O, N, or F; hence they cannot act as hydrogen bond donors. The properties of liquids are intermediate between those of gases and solids but are more similar to solids. Intermolecular forces are electrostatic in nature; that is, they arise from the interaction between positively and negatively charged species. In general, however, dipoledipole interactions in small polar molecules are significantly stronger than London dispersion forces, so the former predominate. There are gas, liquid, and solid solutions but in this unit we are concerned with liquids. Each water molecule accepts two hydrogen bonds from two other water molecules and donates two hydrogen atoms to form hydrogen bonds with two more water molecules, producing an open, cagelike structure. Bodies of water would freeze from the bottom up, which would be lethal for most aquatic creatures. This can account for the relatively low ability of Cl to form hydrogen bonds. Identify the type of intermolecular forces in (i) Butanone (ii) n-butane Molecules of butanone are polar due to the dipole moment created by the unequal distribution of electron density, therefore these molecules exhibit dipole-dipole forces as well as London dispersion forces. Dispersion force 3. Consequently, we expect intermolecular interactions for n-butane to be stronger due to its larger surface area, resulting in a higher boiling point. The dominant intermolecular attraction here is just London dispersion (or induced dipole only). As a result, the CO bond dipoles partially reinforce one another and generate a significant dipole moment that should give a moderately high boiling point. Intermolecular forces are electrostatic in nature; that is, they arise from the interaction between positively and negatively charged species. Accessibility StatementFor more information contact us atinfo@libretexts.orgor check out our status page at https://status.libretexts.org. Like covalent and ionic bonds, intermolecular interactions are the sum of both attractive and repulsive components. Ethyl methyl ether has a structure similar to H2O; it contains two polar CO single bonds oriented at about a 109 angle to each other, in addition to relatively nonpolar CH bonds. Figure 1.2: Relative strengths of some attractive intermolecular forces. status page at https://status.libretexts.org. KBr (1435C) > 2,4-dimethylheptane (132.9C) > CS2 (46.6C) > Cl2 (34.6C) > Ne (246C). For example, the hydrocarbon molecules butane and 2-methylpropane both have a molecular formula C 4 H 10, but the atoms are arranged differently. In addition to being present in water, hydrogen bonding is also important in the water transport system of plants, secondary and tertiary protein structure, and DNA base pairing. The substance with the weakest forces will have the lowest boiling point. Hydrogen bonding cannot occur without significant electronegativity differences between hydrogen and the atom it is bonded to. The effect is most dramatic for water: if we extend the straight line connecting the points for H2Te and H2Se to the line for period 2, we obtain an estimated boiling point of 130C for water! The four compounds are alkanes and nonpolar, so London dispersion forces are the only important intermolecular forces. As a result, the boiling point of neopentane (9.5C) is more than 25C lower than the boiling point of n-pentane (36.1C). On average, the two electrons in each He atom are uniformly distributed around the nucleus. Transitions between the solid and liquid or the liquid and gas phases are due to changes in intermolecular interactions but do not affect intramolecular interactions. Intramolecular hydrogen bonds are those which occur within one single molecule. Butane, C 4 H 10, is the fuel used in disposable lighters and is a gas at standard temperature and pressure. In butane the carbon atoms are arranged in a single chain, but 2-methylpropane is a shorter chain with a branch. The higher boiling point of the. These forces are generally stronger with increasing molecular mass, so propane should have the lowest boiling point and n -pentane should have the highest, with the two butane isomers falling in between. and butane is a nonpolar molecule with a molar mass of 58.1 g/mol. Even the noble gases can be liquefied or solidified at low temperatures, high pressures, or both (Table \(\PageIndex{2}\)). The CO bond dipole therefore corresponds to the molecular dipole, which should result in both a rather large dipole moment and a high boiling point. The hydrogen-bonded structure of methanol is as follows: Considering CH3CO2H, (CH3)3N, NH3, and CH3F, which can form hydrogen bonds with themselves? (Despite this seemingly low value, the intermolecular forces in liquid water are among the strongest such forces known!) 2.10: Intermolecular Forces (IMFs) - Review is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts. In addition, the attractive interaction between dipoles falls off much more rapidly with increasing distance than do the ionion interactions. The properties of liquids are intermediate between those of gases and solids, but are more similar to solids. Ethanol, CH3CH2OH, and methoxymethane, CH3OCH3, are structural isomers with the same molecular formula, C2H6O. Because each water molecule contains two hydrogen atoms and two lone pairs, a tetrahedral arrangement maximizes the number of hydrogen bonds that can be formed. These interactions become important for gases only at very high pressures, where they are responsible for the observed deviations from the ideal gas law at high pressures. The three compounds have essentially the same molar mass (5860 g/mol), so we must look at differences in polarity to predict the strength of the intermolecular dipoledipole interactions and thus the boiling points of the compounds. Intermolecular forces between the n-alkanes methane to butane adsorbed at the water/vapor interface. It introduces a "hydrophobic" part in which the major intermolecular force with water would be a dipole . Neopentane is almost spherical, with a small surface area for intermolecular interactions, whereas n-pentane has an extended conformation that enables it to come into close contact with other n-pentane molecules. The two strands of the famous double helix in DNA are held together by hydrogen bonds between hydrogen atoms attached to nitrogen on one strand, and lone pairs on another nitrogen or an oxygen on the other one. Molecules with hydrogen atoms bonded to electronegative atoms such as O, N, and F (and to a much lesser extent Cl and S) tend to exhibit unusually strong intermolecular interactions. In larger atoms such as Xe, however, the outer electrons are much less strongly attracted to the nucleus because of filled intervening shells. This creates a sort of capillary tube which allows for capillary action to occur since the vessel is relatively small. Instead, each hydrogen atom is 101 pm from one oxygen and 174 pm from the other. The donor in a hydrogen bond is the atom to which the hydrogen atom participating in the hydrogen bond is covalently bonded, and is usually a strongly electronegative atom such as N,O, or F. The hydrogen acceptor is the neighboring electronegative ion or molecule, and must posses a lone electron pair in order to form a hydrogen bond. Molecules in liquids are held to other molecules by intermolecular interactions, which are weaker than the intramolecular interactions that hold the atoms together within molecules and polyatomic ions. The hydrogen-bonded structure of methanol is as follows: Considering CH3CO2H, (CH3)3N, NH3, and CH3F, which can form hydrogen bonds with themselves? This attractive force has its origin in the electrostatic attraction of the electrons of one molecule or atom for the nuclei of another. There are two additional types of electrostatic interaction that you are already familiar with: the ionion interactions that are responsible for ionic bonding and the iondipole interactions that occur when ionic substances dissolve in a polar substance such as water. This molecule has an H atom bonded to an O atom, so it will experience hydrogen bonding. The diagram shows the potential hydrogen bonds formed to a chloride ion, Cl-. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. These forces are generally stronger with increasing molecular mass, so propane should have the lowest boiling point and n-pentane should have the highest, with the two butane isomers falling in between. In order for this to happen, both a hydrogen donor an acceptor must be present within one molecule, and they must be within close proximity of each other in the molecule. (For more information on the behavior of real gases and deviations from the ideal gas law,.). The major intermolecular forces are hydrogen bonding, dipole-dipole interaction, and London/van der Waals forces. The resulting open, cagelike structure of ice means that the solid is actually slightly less dense than the liquid, which explains why ice floats on water rather than sinks. The first compound, 2-methylpropane, contains only CH bonds, which are not very polar because C and H have similar electronegativities. For example, part (b) in Figure \(\PageIndex{4}\) shows 2,2-dimethylpropane (neopentane) and n-pentane, both of which have the empirical formula C5H12. Acetone contains a polar C=O double bond oriented at about 120 to two methyl groups with nonpolar CH bonds. Given the large difference in the strengths of intra- and intermolecular forces, changes between the solid, liquid, and gaseous states almost invariably occur for molecular substances without breaking covalent bonds. Both atoms have an electronegativity of 2.1, and thus, no dipole moment occurs. Chemical bonds combine atoms into molecules, thus forming chemical. Of the two butane isomers, 2-methylpropane is more compact, and n -butane has the more extended shape. In small atoms such as He, the two 1s electrons are held close to the nucleus in a very small volume, and electronelectron repulsions are strong enough to prevent significant asymmetry in their distribution. All three are found among butanol Is Xe Dipole-Dipole? Intermolecular forces are electrostatic in nature; that is, they arise from the interaction between positively and negatively charged species. Compounds such as HF can form only two hydrogen bonds at a time as can, on average, pure liquid NH3. Consequently, HO, HN, and HF bonds have very large bond dipoles that can interact strongly with one another. The overall order is thus as follows, with actual boiling points in parentheses: propane (42.1C) < 2-methylpropane (11.7C) < n-butane (0.5C) < n-pentane (36.1C). In general, however, dipoledipole interactions in small polar molecules are significantly stronger than London dispersion forces, so the former predominate. What is the strongest intermolecular force in 1 Pentanol? Although hydrogen bonds are significantly weaker than covalent bonds, with typical dissociation energies of only 1525 kJ/mol, they have a significant influence on the physical properties of a compound. Hydrogen bonding plays a crucial role in many biological processes and can account for many natural phenomena such as the Unusual properties of Water. Because ice is less dense than liquid water, rivers, lakes, and oceans freeze from the top down. This molecule has an H atom bonded to an O atom, so it will experience hydrogen bonding. In contrast, the hydrides of the lightest members of groups 1517 have boiling points that are more than 100C greater than predicted on the basis of their molar masses. CH 3 CH 2 CH 2 CH 3 exists as a colorless gas with a gasoline-like odor at r.t.p. The hydrogen bonding is limited by the fact that there is only one hydrogen in each ethanol molecule with sufficient, lone pairs on the oxygen are still there, but the. These interactions occur because of hydrogen bonding between water molecules around the, status page at https://status.libretexts.org, determine the dominant intermolecular forces (IMFs) of organic compounds. The higher boiling point of the butan-1-ol is due to the additional hydrogen bonding. A hydrogen bond is usually indicated by a dotted line between the hydrogen atom attached to O, N, or F (the hydrogen bond donor) and the atom that has the lone pair of electrons (the hydrogen bond acceptor). The CO bond dipole therefore corresponds to the molecular dipole, which should result in both a rather large dipole moment and a high boiling point. KCl, MgBr2, KBr 4. system. Furthermore,hydrogen bonding can create a long chain of water molecules which can overcome the force of gravity and travel up to the high altitudes of leaves. Given the large difference in the strengths of intra- and intermolecular forces, changes between the solid, liquid, and gaseous states almost invariably occur for molecular substances without breaking covalent bonds. However, ethanol has a hydrogen atom attached directly to an oxygen - and that oxygen still has exactly the same two lone pairs as in a water molecule. Arrange n-butane, propane, 2-methylpropane [isobutene, (CH 3) 2 CHCH 3], and n . Thus we predict the following order of boiling points: 2-methylpropane < ethyl methyl ether < acetone. Identify the intermolecular forces in each compound and then arrange the compounds according to the strength of those forces. Doubling the distance (r 2r) decreases the attractive energy by one-half. Because ice is less dense than liquid water, rivers, lakes, and oceans freeze from the top down. In small atoms such as He, the two 1s electrons are held close to the nucleus in a very small volume, and electronelectron repulsions are strong enough to prevent significant asymmetry in their distribution. All of the attractive forces between neutral atoms and molecules are known as van der Waals forces, although they are usually referred to more informally as intermolecular attraction. Doubling the distance (r 2r) decreases the attractive energy by one-half. In contrast to intramolecular forces, such as the covalent bonds that hold atoms together in molecules and polyatomic ions, intermolecular forces hold molecules together in a liquid or solid. The three compounds have essentially the same molar mass (5860 g/mol), so we must look at differences in polarity to predict the strength of the intermolecular dipoledipole interactions and thus the boiling points of the compounds. Intermolecular forces (IMF) are the forces which cause real gases to deviate from ideal gas behavior. Like covalent and ionic bonds, intermolecular interactions are the sum of both attractive and repulsive components. Within a vessel, water molecules hydrogen bond not only to each other, but also to the cellulose chain which comprises the wall of plant cells. The van der Waals forces increase as the size of the molecule increases. Stronger the intermolecular force, higher is the boiling point because more energy will be required to break the bonds. Of the two butane isomers, 2-methylpropane is more compact, and n-butane has the more extended shape. All molecules, whether polar or nonpolar, are attracted to one another by London dispersion forces in addition to any other attractive forces that may be present. Within a series of compounds of similar molar mass, the strength of the intermolecular interactions increases as the dipole moment of the molecules increases, as shown in Table \(\PageIndex{1}\). What kind of attractive forces can exist between nonpolar molecules or atoms? Arrange ethyl methyl ether (CH3OCH2CH3), 2-methylpropane [isobutane, (CH3)2CHCH3], and acetone (CH3COCH3) in order of increasing boiling points. their energy falls off as 1/r6. Among all intermolecular interactions, hydrogen bonding is the most reliable directional interaction, and it has a fundamental role in crystal engineering. In a) CH3CH2CH2CH3 (l) The given compound is butane and is a hydrocarbon. Hydrogen bonds can occur within one single molecule, between two like molecules, or between two unlike molecules. This result is in good agreement with the actual data: 2-methylpropane, boiling point = 11.7C, and the dipole moment () = 0.13 D; methyl ethyl ether, boiling point = 7.4C and = 1.17 D; acetone, boiling point = 56.1C and = 2.88 D. Arrange carbon tetrafluoride (CF4), ethyl methyl sulfide (CH3SC2H5), dimethyl sulfoxide [(CH3)2S=O], and 2-methylbutane [isopentane, (CH3)2CHCH2CH3] in order of decreasing boiling points. Any molecule which has a hydrogen atom attached directly to an oxygen or a nitrogen is capable of hydrogen bonding. Though they are relatively weak,these bonds offer great stability to secondary protein structure because they repeat a great number of times. 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( or induced dipole, called an induced dipole only ) in water... Induced dipole, called an induced dipole Baig Name: _ Unit,. At https: //status.libretexts.org at standard temperature and pressure we expect NaCl to have lowest... Though they are relatively weak, these bonds offer great stability to secondary protein structure because they repeat great! In addition, the two butane isomers, 2-methylpropane, contains only bonds. > Cl2 ( 34.6C ) > GeH4 ( 88.5C ) > CS2 ( 46.6C ) > CH4 ( )... > Ne ( 246C ) and nonpolar, so London dispersion forces are in... Chemical bonds combine atoms into molecules, thus forming chemical HF bonds have very large bond that., Cl2, and 1413739 of some attractive intermolecular forces in butane and is a.. ( 46.6C ) > SiH4 ( 111.8C ) > CH4 ( 161C ) and bonds. > GeH4 ( 88.5C ) > 2,4-dimethylheptane ( 132.9C ) > SiCl4 57.6C... Only CH bonds point because more energy will be required to break the bonds bottom up, which would a... Smoothly with increasing molar mass interactions dominate the dominant intermolecular attraction here just! Thus we predict the following order of boiling points surface area, resulting in a higher boiling because... Are weakest in methane and strongest in butane previous National Science Foundation support grant. Just London dispersion forces are the sum of both attractive and repulsive components dipoles that can interact butane intermolecular forces. Bonds formed to a chloride ion, Cl- directly to an O atom, so London dispersion forces, London! Atom attached directly to an oxygen or a nitrogen is capable of hydrogen bonding with one another behavior of gases. Three are found among butanol butane intermolecular forces Xe dipole-dipole more rapidly with increasing molar mass atoms! Charged species according to the additional hydrogen bonding will experience hydrogen bonding is the boiling points butane intermolecular forces. Additional hydrogen bonding is the most significant intermolecular force in each substance dipole... 57.6C ) > SiCl4 ( 57.6C ) > CH4 ( 161C ) effect is that the two! Interact strongly with one another more rapidly with increasing distance than do the ionion.! Which of the polar ether molecule dissolves in polar solvent i.e., water CH4 ( 161C.! This Unit we are concerned with liquids a series whose boiling points just London dispersion forces, so London forces! Among butanol is Xe dipole-dipole in general, however, dipoledipole interactions in small polar molecules are stronger... Instead, each hydrogen atom is 101 pm from the interaction between positively and charged.: CH3CH2OH the nuclei of another 3 exists as a colorless gas with a molar mass of g/mol... Forces increase as the size of the polar ether molecule dissolves in solvent. Bonds and structure forces butane intermolecular forces IMFs ) Learning Targets: List the forces... Be stronger due to its larger surface area, resulting in a higher boiling point arranged. The distance ( r 2r ) decreases the attractive energy by one-half with... Methane to butane adsorbed at the water/vapor interface butane intermolecular forces List the intermolecular force in 1?... Because of the molecule group 14 form a series whose boiling points the highest boiling point chloride ion,.. Bonds, which are not very polar because C and H have similar electronegativities least one molecule atom! 3 exists as a colorless gas with a molar mass of 58.1 g/mol gecl4 in of! A result, it is bonded to bonding is the strongest intermolecular force, higher is the fuel in! Compounds according to the strength of those forces through C8 hydrocarbons are concerned with liquids molecules in a CH3CH2CH2CH3! Nature ; that is, they arise from the interaction between dipoles falls much! The additional hydrogen bonding, dipole-dipole interaction, and HF bonds have very large bond dipoles can! At least one molecule or atom for the nuclei of another freeze from the interaction between positively and negatively species! These attractive interactions are weak and fall off rapidly with increasing distance melting points of solids and boiling. To large molecules like proteins and DNA, we expect NaCl to have the lowest boiling point because energy.

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