Dipole Moment

12 Key excerpts on "Dipole Moment"

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  eBook - ePub

  Introductory Organic Chemistry and Hydrocarbons

  A Physical Chemistry Approach

  • Caio Lima Firme(Author)
  • 2019(Publication Date)
  • CRC Press

    (Publisher)

  Chapter Eleven

  Intermolecular Interactions

  Dipole Moment

  Dipole Moment, μ, is a vector physical quantity (i.e., it needs direction and magnitude to describe it) and a unimolecular/microscopic property (i.e., it needs only one molecule to obtain its value theoretically). Its vector points towards the negative charge from the positive charge (Fig. 11.1(A) ) and it is the product of displacement vector, r, and charge, q. The Dipole Moment vector arises from the electronegativity difference between the bonding atoms. The more electronegative atom has the partial negative charge and the less electronegative atom has the partial positive charge.

  μ →

    =  

  r →

    ⋅   q

  The unit for Dipole Moment is Debye, which is historically defined as 10−10 esu. Å, where esu means electrostatic unit of charge. The atomic (or elementary) charge is 1.602 × 10−19 Coulomb or 4.8 × 10−10 esu (or statcoulombs). For example, for a chemical bond having 0.2 esu of positive and negative charges separated by 1.54 Å:

  μ →

    =   ( 0.2   ×   4.8     ×  

  10

  − 10

  )   ×   ( 1.54 )   =   1.48   D

  In SI units the Dipole Moment is given by C m, where 1 D = 3.336 × 10−19 C m. Then, the Dipole Moment of NaCl (each ion having a unit charge) separated at distance 1.874 Å (where 1 Å = 10−10 m) is:

  μ   =  

  1.602   ×  

  10

  − 19

    ×   1.874   ×  

  10

  − 10

  3.336   ×  

  10

  − 30

    =   9 D

  For heteronuclear diatomic molecules, there is a single Dipole Moment vector, for example, in NO, CO, HBr, etc. Figure 11.1(B) shows the electron charge concentrated in fluorine atom (having negative partial charge) in HF. For homonuclear diatomic molecules, there is no Dipole Moment vector because both nuclei are equal and then there is no difference of electronegativity between then, for example, in H2 , N2 , O2 , Cl2 , etc. Figure 11.1(C) shows that the electron charge is equally distributed between both fluorine atoms in F2

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  Fundamentals of Atomic Force Microscopy

  Part I: Foundations

  • Ronald Reifenberger(Author)
  • 2015(Publication Date)
  • WSPC

    (Publisher)

  −8 cm. This leads to the unit of a Debye for atomic or molecular Dipole Moments:

  As an example, a molecule with a net displacement of 0.2|e− | through a distance of 0.1 nm has a Dipole Moment of 3·2 × 10−30 C · m or about 1D.

  Rather than calculating the Dipole Moment from the charge distribution throughout a molecule, it is sometimes useful to characterize the Dipole Moment associated with various chemical bonds (bond dipoles). For reference, approximate values for permanent Dipole Moments associated with various bond dipoles are listed in Table 2.2 .

  Table 2.2 Permanent dipole bond moments for representative chemical bonds.

  Bond	Bond Dipole Moments (D)
  H–C	0.30
  C–N	0.22
  C–O	0.86
  C–I	1.29
  H–N	1.31
  C–Br	1.48
  C–F	1.51
  H–O	1.53
  C–Cl	1.56
  C=O	2.40
  C≡N (cyano)	3.60

  Fig. 2.11 The dependence of boiling point on molecular Dipole Moment for common solvents. The data points are for propane (C3 H8 ), dimethyl ether (CH3 OCH3 ), chloromethane (CH3 Cl), acetaldehyde (C2 H4 O), and acetonitrile (C2 H3 N).

  As we shall see in the next chapter, molecular Dipole Moments are critically important for describing molecule–molecule interactions and they play an important role when selecting solvents. The near-field local electric fields generated by molecular dipoles are often sufficiently strong to remove atoms from compounds with high melting temperatures. As an example, common table salt (NaCl) is known to melt at 1074K (800°C) yet it readily dissolves at room temperature in water, a polar solvent having a molecular Dipole Moment of 1.8 D.

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  Klein's Organic Chemistry

  • David R. Klein(Author)
  • 2020(Publication Date)
  • Wiley

    (Publisher)

  The Dipole Moment (μ) is used as an indicator of polarity, where μ is defined as the amount of partial charge (δ) on either end of the dipole multiplied by the distance of separation (d ): μ = δ × d PRACTICE the skill APPLY the skill need more PRACTICE? 30 CHAPTER 1 A Review of General Chemistry Partial charges (δ+ and δ−) are generally on the order of 10 −10 esu (electrostatic units) and the distances are generally on the order of 10 −8 cm. Therefore, for a polar compound, the Dipole Moment (μ) will generally have an order of magnitude of around 10 −18 esu ⋅ cm. The Dipole Moment of chloromethane, for example, is 1.87 × 10 −18 esu ⋅ cm. Since most compounds will have a Dipole Moment on this order of magnitude (10 −18 ), it is more convenient to report Dipole Moments with a new unit, called a debye (D), where 1 debye = 10 −18 esu ⋅ cm Using these units, the Dipole Moment of chloromethane is reported as 1.87 D. The debye unit is named after Dutch scientist Peter Debye, whose contributions to the fields of chemistry and physics earned him a Nobel Prize in 1936. Measuring the Dipole Moment of a particular bond allows us to calculate the percent ionic character of that bond. As an example, let’s analyze a C  Cl bond. This bond has a bond length of 1.772 × 10 −8 cm, and an electron has a charge of 4.80 × 10 −10 esu. If the bond were 100% ionic, then the Dipole Moment would be μ = e × d = (4.80 × 10 −10 esu) × (1.772 × 10 −8 cm) = 8.51 × 10 −18 esu ⋅ cm or 8.51 D. In reality, the bond is not 100% ionic. The experimentally observed Dipole Moment is measured at 1.87 D, and we can use this value to calculate the percent ionic character of a C  Cl bond: 1.87 D 8.51 D 22% × 100% = Table 1.4 shows the percent ionic character for a few of the bonds that we will frequently encounter in this text. Take special notice of the C   O bond. It has considerable ionic character, rendering it extremely reactive.

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  Theory of Electric Polarization

  Dielectrics in Static Fields

  • Bozzano G Luisa(Author)
  • 2012(Publication Date)
  • Elsevier Science

    (Publisher)

  We then have: m = le. (1.2) Therefore, the electric moment of a system of charges with zero net charge is generally called the electric Dipole Moment of the system. A simple case is a system consisting of only two point charges +e and — e at a distance I. Such a system is called a (physical) electric dipole, its moment is equal to el, the vector / pointing from the negative to the positive charge. In theoretical organic chemistry the dipole vector is generally taken as pointing from the positive to the negative charge. We prefer to use the physical definition given above. A mathematical abstraction derived from the above defined physical dipole is the ideal or point dipole. Its definition is as follows: the distance / between two point charges + e and — e is replaced by l/n and the charge e by en. The limit approached as the number η tends to infinity is the ideal dipole. The equations derived for ideal dipoles are much simpler than those obtained for non-ideal dipoles. Many neutral molecules are examples of charge systems with a non-ideal electric Dipole Moment, since in most types of molecule the centres of gravity of the positive and negative charge distributions do not coincide. Apart from these permanent or intrinsic Dipole Moments, a temporary or induced Dipole Moment arises when a particle is brought into an external electric field. Under the influence of this field the positive and negative charges in the particle are moved apart: the particle is polarized. In general, these induced dipoles can be treated as ideal; permanent dipoles, however, may generally not be treated as ideal when the field at molecular distances is to be calculated (see section 2). ELECTRIC DIPOLES AND MULTIPOLES 11 The values of molecular Dipole Moments are usually expressed in Debye units. The Debye unit, abbreviated as D, equals 1 0 1 8 electrostatic units (e.s.u.). The permanent Dipole Moments of non-symmetrical molecules generally lie between 0.5 and 5D.

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  Handbook of Magnetism

  • (Author)
  • 2014(Publication Date)
  • Learning Press

    (Publisher)

  Molecular dipoles Many molecules have such Dipole Moments due to non-uniform distributions of positive and negative charges on the various atoms. Such is the case with polar compounds like hydroxide (OH − ), where electron density is shared unequally between atoms. A molecule with a permanent Dipole Moment is called a polar molecule. A molecule is polarized when it carries an induced dipole. The physical chemist Peter J. W. Debye was the first scientist to study molecular dipoles extensively, and, as a consequence, Dipole Moments are measured in units named debye in his honor. With respect to molecules, there are three types of dipoles: • Permanent dipoles : These occur when two atoms in a molecule have subs-tantially different electronegativity: One atom attracts electrons more than another, becoming more negative, while the other atom becomes more positive. • Instantaneous dipoles : These occur due to chance when electrons happen to be more concentrated in one place than another in a molecule, creating a temporary dipole. • Induced dipoles : These can occur when one molecule with a permanent dipole repels another molecule's electrons, inducing a Dipole Moment in that molecule. More generally, an induced dipole of any polarizable charge distribution ρ (remember that a molecule has a charge distribution) is caused by an electric field external to ρ . This field may, for instance, originate from an ion or polar molecule in the vicinity of ρ or may be macroscopic (e.g., a molecule between the plates of a charged capacitor). The size of the induced dipole is equal to the product of the strength of the external field and the dipole polarizability of ρ . Typical gas phase values of some chemical compounds in debye units: • carbon dioxide: 0 • carbon monoxide: 0.112 • ozone: 0.53 • phosgene: 1.17 • water vapor: 1.85 • hydrogen cyanide: 2.98 • cyanamide: 4.27

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  Dielectrics in Time-Dependent Fields

  • Bozzano G Luisa(Author)
  • 2012(Publication Date)
  • Elsevier Science

    (Publisher)

  CHAPTER XIV THE EXPERIMENTAL DETERMINATION OF PERMANENT DIPOLE AND QUADRUPOLE MOMENTS §88. Introduction One of the main applications of dielectric theory in physics and chemistry is still the determination of permanent Dipole Moments of molecules. These values can be of great use, in both o r g a n i c 1 -3 and inorganic 4 chemistry, for the elucidation of molecular structures, since in a certain approximation the Dipole Moment can be considered to be composed of contributions from the different bonds in the molecule: μ =Σ*> (14.1) i where the bond moment μ, of a bond is taken to be the same in different molecules. For this reason, if a choice has to be made between different possible structures of a compound with a given over-all formula, or between possible conformations of a compound with a given structure, it is often possible to reach a decision by calculating the expected values of the Dipole Moment for the different possible structures or conformations with eqn. (14.1), and com-paring these values with the experimental value. This procedure is especially productive if one of the possible structures or conformations has a centre of symmetry, so that the Dipole Moment for this structure is known to be exactly zero. Another application of Dipole Moments is in the study of the chemical bond, since the Dipole Moment gives information about the change in the electron distribution in the molecule that accompanies the realization of such b o n d s . 3 ,4 This is of special interest with respect to coordination complexes in inorganic chemistry and charge transfer complexes in organic chemistry, 3 ,5 where the determination of the Dipole Moment often helps to establish the existence of the complex. A third application of Dipole Moments of molecules is in the calculation of the molecular interaction energy in imperfect gases and in liquids, 6 as pointed out in section 16.

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  Handbook of Nanophysics

  Clusters and Fullerenes

  • Klaus D. Sattler(Author)
  • 2010(Publication Date)
  • CRC Press

    (Publisher)

  10 -1 10.1 Introduction This chapter discusses the behavior and detection of electric and magnetic Dipole Moments in atomic and molecular nano-clusters. We concentrate on studies of free particles (i.e., clus-ters produced, probed, mass selected, and detected in beams [Pauly 2000]), because in such work the focus is on exploring the inherent physical properties of these nanoparticles. In this way, clusters can be studied with their size and composition pre-cisely known, and with their features unperturbed by substrate interactions. A fundamental characteristic of a molecule or nanoparticle is the arrangement and distribution of electrical charges within it, as well as that of electronic orbital and spin angular momenta. Electric and magnetic Dipole Moments are observables, which directly reflect these distributions, and are, therefore, very use-ful experimental parameters for the direct assessment of models and theories of particle structure, bonding, and internal dynam-ics. In addition, of course, polar and magnetic nanoclusters carry significant practical promise as building blocks for materials with novel magnetic and ferroelectric properties. Although the principles underlying electric and magnetic ordering in nanoclusters may be distinct, the experimental signatures of such ordering in cluster beam work have a lot in common, in particular, the patterns of beam deflection under the influence of externally applied fields. It is for this reason that they are discussed jointly in this chapter. 10.2 Definitions As a starting point, it is appropriate to cite the textbook expres-sion for the total electric Dipole Moment: = ρ ∫ 3 ( ) d . p r r r (10.1) Here ρ ( ) r is the charge density (including both electrons and nuclei) at position r within the particle, and the integral is over the entire particle volume.

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  Molecular Physics

  • Dudley Williams(Author)
  • 2013(Publication Date)
  • Academic Press

    (Publisher)

  7. ELECTRIC PROPERTIES OF MOLECULES* A great many molecular phenomena have their origin in the electric properties of individual molecules. The most important electric proper-ties of a neutral molecule are its permanent Dipole Moment and polariza-bility. Through these the molecular motion is coupled to external electric fields giving rise to a host of effects including: absorption, emission, and scattering of radiation; refraction of light, polarization of dielectrics, and Stark effect. Absorption, emission and scattering of radiation were dis-cussed in Part 2. Refraction, polarization of dielectrics, and Stark effect are discussed in this part. Of the higher electric multipole moments only the molecular quadrupole can be singled out as producing observable effects. These are discussed in Chapter 7 .4. f An additional phenomenon which can be attributed to a characteristic of the molecular charge distribution which is not revealed by the lower multipole moments is optical activity. Optical activity is discussed in Chapter 7 .5. When atoms unite to form a molecule the atomic charge distributions are altered to such an extent that a permanent molecular Dipole Moment frequently results. This Dipole Moment is a vector quantity with com-ponents defined by equations of the form where qi is the charge on the ith particle, and Xi is its x coordinate. Mole-cules with permanent Dipole Moments are called polar molecules. If a polar molecule is placed in a static electric field it will be subject to a torque tending to align its Dipole Moment in the field direction. In addi-tion to exerting a torque on the molecule the electric field will slightly distort the molecular charge distribution and produce an induced Dipole Moment. The magnitude of this induced Dipole Moment depends on the structure of the molecule, the magnitude of the electric field, and the t See also Vol. 1, Chapter 8.5; Vol. 2, Section 10.6.3; and Vol. 6, B, Chapter 7.1.

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  Electrical, Optical and Magnetic Properties of Nucleic acid and Components

  • J Duchesne(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  Because of the possibility that the Dipole Moment of a molecule causes the latter to form aggregates and to undergo solvation, especially in polar solvents, the Dipole Moments are measured either in the gas phase—which is mainly done for small molecules—or in solution in non-polar solvents. This is a 1 2 Ε. D. BERGMANN AND Η. WEILER-FEILCHENFELD serious limitation specifically for such relatively complex molecules as pyrimidines, purines or their derivatives which occur in nature. It should be mentioned that recently (Myers and Sun, 1966) a method has been suggested to derive the Dipole Moments from measurements in mixtures of polar and non-polar solvents, but this method has not yet found wider application, though it opens many new possibilities. Modern quantum-chemical methods have made it possible to calculate the Dipole Moments of even complex molecules (Pullman and Pullman, 1952). In these cases, the total Dipole Moment is separated into that stemming from the distribution of the ^-electrons and that representing the polarisation of the -bonds, these two being calculated independently. In both calculations, the geometry of the molecule, inter alia, has to be known or at least guessed well; such guesses can be improved by iterative procedures. It has been found that the method of linear combination of atomic orbitals (LCAO) gives generally good agreement between theory and experiment and that more refined methods of calculation do not substantially improve that agreement.

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  Collected Works Of Lars Onsager, The (With Commentary)

  (With Commentary)

  • Per Chr Hemmer, Helge Holden, Signe Kjelstrup(Authors)
  • 1996(Publication Date)
  • World Scientific

    (Publisher)

  Further pertinent characteristics of a molecule are its polarizability. a, related to an internal refractive index n as follows »' - 1 »« + 2' (3) and a permanent electric moment IM> {in vacua). In an electric field, F, the total electric moment, (») Wymu. THIS JOOBMAL. M, 1482 (1938). 678 1488 LARS ONSAGER Vol.58 is the vector sum of the permanent and the induced Dipole Moments m - M*i + oF (4) where u denotes a unit vector in the direction of the dipole axis. The statistical a priori expecta-tion of u is isotropic. First, let us consider an unpolarized medium of dielectric constant, t, and introduce a rigid dipole of moment m into a cavity of radius a. For simplicity, let the dipole be a point singularity of the electric field, situated in the center of the spherical cavity. The potential The solution of this problem is . iu cos 9 _ . , , - j Rr cos 9, (r < a) , m* cos 9 . . . (6) whereby the coefficients m* and R must equal * 3. * m zT+~i m 2(« - 1) m 2« + 1 a« (7) The former may be called the external moment of the immersed dipole; it determines the force (modified by the intervening medium), which the dipole will exert upon a distant charge in the di-electric. The coefficient R measures the electric field which acts upon the dipole as a result of electric displacements induced by its own pres-ence, we shall refer to it as the reaction field. For a neutral, spherical molecule with an arbi-trary distribution of charges the above relations between m, m* and 2? still maintain. In this more general case m is the actual Dipole Moment of the molecule, while m* measures the dipole part of its external field, and R the homogeneous part of the reaction field.

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  Molecular Properties V4

  • Douglas Henderson(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  Perhaps the most helpful model yet devised for interpreting and utiliz-ing Dipole Moments is that of the bond, or group, dipole. The model treats the molecule as if it were comprised of a number of noninteracting bonds or groups, so IV· Interpretation of Electric Moments (4.1) Tables of bond moments are available in textbooks (see those mentioned T A B L E II SELECTED VALUES FOR D I P O L E AND Q U A D R U P O L E M O M E N T S 0 . Dipole m o m e n t ^ „ Quadrupole m o m e n t ^ _ Substance* Ref. ^ J* 2 e Ref. (D) (in 1 0 _ 2e esu) 2 p z H a t o m 0 — -1 6 . 1 4 Buckingham (1959b) 3d 2 2 H atom 0 — -4 8 . 4 2 Buckingham (1959b) H 2 + 0 — 2.06 Bates and Poots (1953)« H 2 0 — 0.651 I Wolniewicz (1966), 2 ' [ Stogryn and Stogryn (1966) H 2 (v = l) 0 — 0 721 I W o l n i e w i c z ( 1966 )> 2 ' Stogryn and Stogryn (1966) D 2 0 — 0.643 Wolniewcicz (1966) H D 1.54 χ ΙΟ 3 ( H + D -) , Kolos and Wolniewicz (1966) 6 5.8 5 χ 1 0 -4 Trefler and G u s h (1968) 0.647 — 7 L i H 5.882 ± 0.003 W h a r t o n et al. (1960) - 5 Stogryn and Stogryn (1966) 7 L i H (v = 1) 5.990 ± 0.003 W h a r t o n et al (1960) - 5 Stogryn and Stogryn (1966) 6 L i H 5.884 ± 0.003 W h a r t o n et al. (1960) - 5 Stogryn and Stogryn (1966) L i 2 0 — 13.8 Stogryn and Stogryn (1966) N 2 0 — - 1.4 Buckingham et al. (1968) 0 2 0 — - 0.4 Buckingham et al. (1968) C O 0.112 ( C -0 + ) Nelson et al. (1967), 0.4 e Buckingham et al. (1968) Rosenblum et al. (1958) C O ( a 3 7 7 ) 1.38 Freund and Klemperer (1965) — — N O 0.153 Nelson et al. (1967) - 4.2 e Buckingham et al. (1968) S O 1.55 Nelson et al. (1967) — — SOCZI) 1.47 Carrington et al. (1967) — — T A B L E II (continued) c , Dipole m o m e n t Quadrupole m o m e n t substance Ref. A r . _ e . Ref. (D) (in 10~ 2β esu) H F 1.8265 M u e n t e r and Klemperer (1970) 2.6 Stogryn and Stogryn (1966) D F 1.8188 M u e n t e r and Klemperer (1970) — — HCl 1.08 Nelson et al. (1967) 3.8 Stogryn and Stogryn (1966) H B r 0.82 Nelson et al.

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  Thermophysical Properties of Chemicals and Hydrocarbons

  • Carl L. Yaws(Author)
  • 2008(Publication Date)
  • William Andrew

    (Publisher)

  The compilations of CRC (2), Daubert and Danner (3), Landolt and Bornstein (6), and Yaws (16-17) were used extensively for the tabulation. Estimates were primarily based on the method of Abraham and Smith (4). The Dipole Moment which involves the first moment of the electric charge density of the compound is used in property correlations for polar compounds. Example In an engineering analysis, the Dipole Moment is needed for chloroform (CHCI3). Determine the Dipole Moment for chloroform. Inspection of the tabulation yields: Dipole Moment = 1.010 Debye References 1. Bondi, A., PHYSICAl PROPERTIES OF MOl EClJl AR CRYSTAl S, I lOLl/OS AND GLASSES, John Wiley and Sons, New York, NY (1968). 2. CRC HANDBOOK OF CHEMISTRY AND PHYSICS, 75th -86th eds., CBC Press, Inc., Boca Baton, FL (1994-2006). 3. Daubert, T. E. and B. P. Danner, DATA COMPII ATiON OF PROPERTIES OF PURE COMPOUNDS, Parts 1, 2,3, and 4, Supplements 1 and 2, DIPPB Project, AIChE, New York, NY (1985-1994). 4. Dixon, S. L. and P. C. Jurs, Atomic Charge Calculations for Quantitative Structure -Property Belationships, J. Comput. Chem., 13, 402 (1992). 5. Hayashi, M. and T. Inagusa, J. Mol. Spec., 138, 135 (1989). 6. Landolt, H. and R. Bornstein, ZAHLENWERTE l JND Fl JNKIONEN ANS PHYSIK CHEMEI, ASTRONOMIE UNO TECHNIK, Springer-Verlag, Heidelberg, Germany (1971-2005). 7. LANGE'S HANDBOOK OF CHEMISTRY, 13th, 14th, and 15th eds., McGraw-Hili, New York, NY (1985, 1992, 1999). 8. Le Fevre, R. J. W DIPOI E MOMENTS, THEIR MEASUREMENT AND APPLICATION IN CHEMISTRY, John Wiley and Sons, New York, NY (1953). 9. McClellan, A. L., TABLES OF EXPERIMENTAL Dipole MomentS, W. H. Freeman Publishing, San Francisco, CA (1963). 10. Nelson, B. D., D. B. Lide, A. Maryotl, National Bureau of Standards, NSBDS 10, Washington, DC (1967). 11. Scappini, F., A. C. Fantoni, and W. Caminati, J. Mol. Spec., 120, 101 (1986). 12. Smyth, C. P., DIEt ECTRIC BEHAVIOR AND STRUCTlJRE, McGraw-Hili Book Co., New York, NY (1955).

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