Questions tagged [dipole]

For questions about the dipole moment of a bond or a molecule; its calculation, comparison with other bonds or molecules, affect on molecular properties, etc.

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Is Hexafluorocyclohexane the “Most Polar” Small Molecule?

Earlier this year, there was a lot of attention when all-cis 1,2,3,4,5,6-hexafluorocyclohexane was synthesized*: Notably, C&E News quoted the lead author: This compound is remarkable for being ...
28
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2answers
11k views

Confusion about direction of dipole arrow in alpha-helices and other molecules

I understand that molecular dipoles are electric dipoles. And electric dipole moment vectors point from the negative to the positive charge. In class we learned to draw these special molecular dipole ...
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2answers
28k views

Why is water a dipole?

Water ($\ce{H2O}$) is a dipole. The reason why is simply because it is not symmetrical, there are more electrons on the oxygen side than on the hydrogen side, and the electronegativity of oxygen. But ...
22
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8k views

Dipole moments of pyrrole and furan

Why do pyrrole and furan have dipoles oriented in different directions?
22
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2answers
10k views

Is Hydrogen Bonding a Type of Dipole Dipole Interaction?

I understand that dipole dipole forces is due to the attraction of the different partials charges of atoms in different molecules due to their different electro-negativities. For hydrogen bonding, ...
19
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2answers
40k views

How does a lone pair of a central atom affect the dipole moment?

Dipole moment is the degree of polarity, i.e. the seperation of positive and negative charges. But I am not getting the intuition why and how lone pairs affect the polarity and dipole moment. I cannot ...
19
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2answers
5k views

Non-zero dipole moment of hydroquinone

Why does hydroquinone possess a non-zero dipole moment? The $\ce{OH}$ groups present at para positions on the benzene ring should cancel the effect of each other... if there is a plane change then ...
18
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3answers
4k views

How to calculate molecular dipole moment from a known wavefunction?

Say I have a molecular wavefunction as a set of molecular orbitals and want to calculate the molecule's dipole moment, but don't know how! I searched a lot but couldn't find any practical example. $$\...
18
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4answers
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What is the origin of the “positive-to-negative” convention concerning dipole moments in chemistry?

I'm a physics professor who often teaches students who have taken a lot of chemistry (read: pre-meds). In physics, the dipole moment of a charge configuration is defined as pointing from ...
17
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2answers
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Dipole moment of cis-2-butene

I need someone to back me up on this before I go confront my teacher: I was doing some analysis of the dipole moment of cis-2-butene. Let's say that the alkyl groups are both on top. Would the dipole ...
15
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1answer
2k views

How to explain the dipole moment anomaly of methyl fluoride and methyl chloride with respect to their hydracids?

I was checking dipole moment orders, and came across a very peculiar result: Methyl fluoride $(\ce{CH3F})$ has lesser dipole moment than methyl chloride ($\ce{CH3Cl}$), but hydrofluoric acid ($\ce{HF}$...
15
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0answers
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How to Calculate Transition Dipole Moment from Two Known Wavefunctions

I am interested in calculating the transition dipole moment (TDM) from the information from two wavefunctions of different states. This is somewhat similar to calculating the molecular dipole moment ...
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Why are dipoles “permanent/induced dipole permanent/induced dipole” and not just “permanent/induced dipole” once?

My teacher would always say "induced dipole induced dipole" and while it annoyed my slightly (as you were saying the same word twice) it didn't really bother me, ...
14
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1answer
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Order of dipole moments

What is the order of dipole moments for $\ce{SO3, SiO2, P2O5,}$ and $\ce{Cl2O7}$? This question is from a book and the answer given is $\ce{Cl2O7 < SO3 < P2O5 < SiO2}$. Can someone explain ...
14
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1answer
440 views

Dipole-quadrupole polarizability term for induced dipole

For describing an induced dipole, I have usually seen the following equation, $$ P_{i} = \alpha_{ij}E_{j} + \frac{1}{2}\beta_{ijk}E_{j}E_{k} $$ where $P_{i}$ is the $i^{\text{th}}$ component of the ...
13
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What is the exact reason that compounds such as carbon dioxide cannot interact with other compounds through dipole-dipole interactions?

Whilst I understand that $\ce{CO2}$ has a linear structure, resulting in a vector sum of the dipoles of 0, I do not understand why the dipoles formed at the two oxygen atoms as a result of their ...
13
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1answer
2k views

Why is the dipole moment of chloromethane larger than the dipole moment of fluoromethane?

On the Pauling electronegativity scale, fluorine and chlorine are 3.98 and 3.16, respectively. Since the dipole moment is dependent on electronegativity, why is the dipole moment of chloromethane ...
13
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1answer
7k views

Is an ionic bond more like a covalent bond or an intermolecular force?

I have asked a question loosely asking this, where I confused terms and did not specify what I wanted to know here, so I formed a new question. What are the differences and similarities between ionic ...
13
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1answer
191 views

Are there any (simple) molecules with very different absorption and emission dipole directions?

When a single molecule absorbs or emits light, it does so perpendicular to the direction of the respective transition dipole. In principle, the directions of the dipoles for absorption and emission ...
12
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2answers
1k views

How to identify hydrogen bonds and other non-covalent interactions from structure considerations?

Chemistry is governed by a wide range of interactions, from ionic and covalent bonding, or other types of strong interactions, towards weaker types of bonding, attraction, or repulsion, that typically ...
12
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2answers
7k views

Does the dipole moment increase or decrease by increasing the bond length?

It is established the dipole moment is a result of multiplication of the magnitude of charges (Q) and the distance between them (r). What I understand is that when an electron and a proton get closer (...
12
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1answer
465 views

Why do post-Hartree-Fock methods fail to predict the direction of the dipole moment of carbon monoxide?

In carbon monoxide the dipole moment (negative to positive) points towards the oxygen, as I explained it in How can the dipole moment of carbon monoxide be rationalised by molecular orbital theory? A ...
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2answers
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Which intermolecular interaction is dependent on the inverse cube of distance?

The intermolecular interaction that is dependent on the inverse cube of distance between molecules is: hydrogen bond ion-ion interaction ion-dipole interaction London force Inverse ...
11
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2answers
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What is the bond angle of water?

I have been trying to find out the bond angle of $\ce{H2O}$, but every site I visit has a different answer. So far, I have found the following angles listed: Site 1: 104.4º Site 2: 107.5º OR 104.5º, ...
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483 views

Hartree-Fock dipole moment

I read this sentence in a paper (J. Phys. Chem. A 2014, 118 (20), 3678–3687. DOI: 10.1021/jp502475e): Calculations using Hartree–Fock theory systematically overestimated dipole moments and ...
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Is carbon dioxide IR inactive?

I am told that carbon dioxide is IR inactive. This somehow strikes me as untrue or at best oversimplified, because yes, it is overall symmetrical, but can't $\ce{CO2}$ be induced to show asymmetric ...
10
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2answers
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Why is CO practically nonpolar?

This question was in my book. According to me CO should be polar as it should have a dipole moment. But I found that the $\sigma$-electron drift from C to O is almost nullified by the $\pi$-electron ...
10
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2answers
750 views

Does 1-bromo-4-chlorobenzene have a permanent dipole moment?

My first thought was there would be a dipole moment as chlorine and bromine are unequal in electronegativity. I have since looked up the electronegativity of both chlorine and bromine through the ...
10
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2answers
30k views

Why is HCl not considered to have hydrogen bonding?

A molecule that has hydrogen bonding usually follows these two premises. 1.) There is a hydrogen atom involved 2.) Hydrogen must be bonded to a highly electronegative element which are ...
9
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1answer
536 views

What is the dipole moment direction in the nitrosonium ion?

In the recent question about the molecular orbitals of $\ce{NO^{$x$}};\ x\in\{-1,0,+1\}$ the follow-up title question arose: Just a random side-question: What’s the dipole moment’s negative and ...
9
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2answers
194 views

Why is ammonia still considered polar despite undergoing rapid inversion?

Here it is stated that a molecule with a rotation axis cannot have dipole moment perpendicular to the axis, as any dipole moment would be changed upon rotation about this axis (which preserves the ...
9
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1answer
242 views

Why do we say “approximation” in the dipole approximation in spectroscopy?

In the dipole approximation, the following relation holds: $$ \hat{V} = -\hat{\mu} \cdot \vec{E}. $$ When we say "approximation", I guess we want to point out that we are dealing with linear ...
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1answer
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Why does C=O have a larger dipole moment than C-O?

Why does $\ce{C=O}$ have a larger dipole moment than $\ce{C-O}$? According to me, dipole moment directly depends upon bond length and electronegativity difference. In $\ce{C=O}$ and $\ce{C-O}$, (I ...
8
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1answer
190 views

Does tetrachlorodibenzo-p-dioxin (2,3,7,8) have a nonzero dipole moment?

I've looked at and drawn the structure, and I originally felt that it would be nonpolar - as I believe all the dipoles would cancel out, but I'm not 100% sure. I might be too dependent on the fact ...
7
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4answers
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Why is tetrafluoromethane non-polar and fluoroform polar?

Consider the Lewis dot structures of the molecules fluoroform, $\ce{CHF3}$, and tetrafluoromethane, $\ce{CF4}$:   My first line of thought is that both of these molecules are symmetrical (the ...
7
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1answer
1k views

Calculating dipole moments from atomic partial charges

How can I calculate dipole moment of a complex molecule where the partial charges are available from density functional theory? I have the coordinates of each atom from atomistic simulations of an ...
7
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3answers
637 views

At what frequency does a non-polar molecule acquire a dipole able to participate in London Dispersion forces?

London Dispersion forces are forces between non-polar non-ionic molecules that the random fluctuation of their electrons makes them temporarily dipoles. What is the frequency that this occurs? Every ...
7
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1answer
70k views

Dipole moment - calculation of percentage ionic character

Question: The dipole moment of $\ce{HBr}$ is $2.60 \times 10^{-30}$ and the interatomic spacing is $1.41$. What is the percentage ionic character of $\ce{HBr}$? What I know is that the percentage ...
7
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1answer
531 views

Why does acetonitrile have a larger dipole moment and boiling point than acetaldehyde?

Experimentally, acetonitrile has a larger dipole moment than acetaldehyde, but I've never understood why. I always thought that the charge separation between carbon/oxygen is larger than that of ...
7
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1answer
131 views

How real are bond dipoles?

In general chemistry, it is common to teach students to determine a molecular dipole by having them first determine "bond dipoles" which are just based on electronegativity. Then, by adding up these ...
6
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2answers
65k views

Why don't polar and non-polar compounds dissolve each other?

Dipoles can also be induced in polar and non polar compounds, then why don't they dissolve?
6
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1answer
198 views

How do atoms lose their induced dipole?

There exists the basic chemistry lesson with induced dipoles where the electron density of one atom changes causing a dipole to form and causing a cascading effect where other atoms adjacent to that ...
6
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1answer
4k views

How do you calculate the dipole moment of larger molecules?

I know that the dipole moment is obtained by: $$ \vec{\mu} = Q \cdot \vec{d} $$ with the condition that charges of a pair of atoms are equal and opposite, i.e. $\ce{NaCl}$. But, in order to obtain ...
6
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3answers
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Why is the dipole moment of ethyl chloride larger than that of vinyl chloride?

The dipole moment of ethyl chloride is 2.10 D (J. Mol. Struct. 1990, 216, 9–26), and that of vinyl chloride is 1.42 D (J. Chem. Phys. 1960, 32 (1), 205–209). Why is this the case? I would have ...
6
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1answer
1k views

Relationship between electric dipole moment and polarization?

$$\vec{p}_\text{ind} = \alpha \vec{E}$$ The induced dipole moment is the polarizability times the electric field vector. $$\vec{P}(\omega) \propto \chi^{(1)}(\omega) \vec{E}(\omega)$$ ...
6
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1answer
93 views

Accuracy benchmarks for atomic multipole moments

Thermochemical accuracy is regularly quoted as 1 kcal mol$^{-1}$, or 4.2 kJ mol$^{-1}$. I'm expressing some data and I want to use benchmarks like this to validate them, however, they are not all in ...
6
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1answer
305 views

Chemical bonding and dipole moment

We know that ammonia undergoes amine inversion. Why doesn't the dipole moment decrease in ammonia, since the direction of the dipole changes to the opposite direction every time there's inversion? ...
6
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1answer
2k views

Trend in the boiling point of the hydrogen halides

The boiling points of the hydrogen halides are as follows: $$\begin{array}{cc} \hline \text{Species} & \text{Boiling point / }\mathrm{^\circ C} \\ \hline \ce{HCl} & -85.1 \\ \ce{HBr} & -...
6
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1answer
517 views

Why are the dispersion forces in CS2 stronger than the dipole-dipole forces in COS?

London dispersion forces supposedly have the least strength out of all the intermolecular forces. But $\ce{CS2}$, which has only dispersion forces, has a higher boiling point (and thus stronger ...
6
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0answers
197 views

Why is the dipole moment of XeF$_6$ zero? [duplicate]

In Concise Inorganic Chemistry by JD Lee (4th edition; adapted by Sudarshan Guha), page 73 under the section 3.6 (VSEPR Theory chapter Chemical Bonding): ...according to this theory, the position ...