What is Chiral: Definition and 91 Discussions

Chirality is a property of asymmetry important in several branches of science. The word chirality is derived from the Greek χειρ (kheir), "hand," a familiar chiral object.
An object or a system is chiral if it is distinguishable from its mirror image; that is, it cannot be superimposed onto it. Conversely, a mirror image of an achiral object, such as a sphere, cannot be distinguished from the object. A chiral object and its mirror image are called enantiomorphs (Greek, "opposite forms") or, when referring to molecules, enantiomers. A non-chiral object is called achiral (sometimes also amphichiral) and can be superposed on its mirror image.
The term was first used by Lord Kelvin in 1893 in the second Robert Boyle Lecture at the Oxford University Junior Scientific Club which was published in 1894:

I call any geometrical figure, or group of points, 'chiral', and say that it has chirality if its image in a plane mirror, ideally realized, cannot be brought to coincide with itself.
Human hands are perhaps the most universally recognized example of chirality. The left hand is a non-superimposable mirror image of the right hand; no matter how the two hands are oriented, it is impossible for all the major features of both hands to coincide across all axes. This difference in symmetry becomes obvious if someone attempts to shake the right hand of a person using their left hand, or if a left-handed glove is placed on a right hand. In mathematics, chirality is the property of a figure that is not identical to its mirror image. A molecule is said to be chiral if its all valence is occupied by different atom or group of atoms.

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  1. S

    I Propagator of massless Weyl field

    I have this Lagrangian for a free massless left Weyl spinor, so it’s just the kinetic term, that can be written embedding the field into a larger Dirac spinor and then taking the left projector in this way: $$i \bar{\psi} \cancel{\partial} P_L \psi$$ Srednicki says that the momentum space...
  2. Mark Harder

    I Chiral symmetries in E[SUP]^n[/SUP]

    As a biochemist, I deal with chirality of molecules all the time. If you have a tetrahedral molecule, for example a carbon atom, and all 4 vertices are labeled differently, as in different atoms on each one, then that molecule has a mirror-symmetric one that cannot be superimposed on the...
  3. T

    I Why is K an anti-unitary operator in (26)?

    Hey all, I just wanted to double check my understanding of (26) in the following notes: https://arxiv.org/pdf/1512.08882.pdf. Is the reason that ##(U_{T}\cdot K) \cdot (U_{C}\cdot K) = U_{T}\cdot U_{C}^{*}## because ##K## is a unitary operators and thus ##(K\cdot U_{C}\cdot K) = U_{C}^{*}## as...
  4. B

    A Question about chiral molecules

    Hello! I started reading a bit about chiral molecules, and I have some questions. For reference, I will use this article for my questions. In Figure 1 in that article they show the energy levels for a typical chiral molecule (my question is for the case in which the left/right enantiomers are...
  5. I

    Chiral Column Chromatography

    "Resolution of enantiomers can be accomplished using column chromatography. When enantiomers are passed through a traditional column, they travel at the same rate because their properties are identical. However, if a chiral adsorbent is used, the enantiomers interact with the adsorbent...
  6. E

    Polarisation through a chiral nematic crystal

    If light passes into a birefringent material with constant fast and slow directions, ##\hat{x}## and ##\hat{y}##, that are oriented the same way at any point in the crystal, then the electric field is$$\vec{E}(z,t) = E_0\hat{x}\cos{(\theta_0)}e^{i\omega(t - \frac{n_x}{c}z)} +...
  7. B

    I What is the electric charge of a neutrino?

    Hello! I am a bit confused about neutrinos in the standard model. The vertex of the weak interaction charged current, implies that any neutrino interacting through the charged current must be left handed. However the neutral current allows coupling to the right handed particles, too (and we see...
  8. bob012345

    I Meaning of the Orbital Angular Momentum of Super Chiral Light

    In this article it discusses the generation of something called super chiral light and claims with metamaterials they can make it have very high angular momentum like l=100. What does that really mean? How does that relate in magnitude to the normally computed linear momentum of a photon p=h/λ...
  9. H

    I Right chiral vs left chiral electrons in the standard model

    Sometimes I hear particle physicists refer to left/right chiral electrons as different particles that are 'mixed' by the mass term. Maybe I misunderstood entirely, but if there is even a handwavy sense in which this is the case, clarifications would be appreciated. In high energy collisions...
  10. K

    I What is the origin of the non-existence of right handed chiral neutrinos?

    Hello! I am a bit confused about the non-existence of right handed chiral neutrinos. Is this and experimental fact, or it follows from the theory directly? And if it is experimental, how can one test that? Can the chirality be measured? Thank you!
  11. D

    How to explain the phenomenon of optical rotation of chiral?

    I am Professor of Inorganic Chemistry of the State University of Southwest of Bahia - UESB. I have a PhD from UFMG in Natural Product Chemistry. I use the polarimeter in my experiments and would like to understand what happens on a micro scale (chiral molecules) to provide the phenomenon of...
  12. P

    Dirac Lagrangian invariance under chiral transformation

    Consider the Dirac Lagrangian, L =\overline{\psi}\left(i\gamma^{\mu}\partial_{\mu}-m\right)\psi, where \overline{\psi}=\psi^{\dagger}\gamma^{0} , and show that, for \alpha\in\mathbb{R} and in the limit m\rightarrow0 , it is invariant under the chiral transformation...
  13. J

    Chemistry Simple elementary question chiral molecule

    Homework Statement Find if a molecule is chiral or not. It is 2-chloropentane Homework Equations IF the mirror image is superimposable to the molecule it is not chiral. The Attempt at a Solution Well I wrote the structural formula in 2D and I thought it was not chiral.(bottom ) But the book...
  14. C

    I Spontaneous symmetry breaking of chiral symmetry

    The quark sector of the QCD lagrangian can be written as (restricting to two flavours) $$\mathcal L = \sum_{i=u,d} \bar q_i ( i \gamma_{\mu} D^{\mu} + m) q_i .$$ Write ##q = (u d)^T## and $$M = \begin{pmatrix} m_u & 0 \\ 0 & m_d \end{pmatrix}$$ Given that the masses of the u and d quarks are...
  15. P

    I Why is the 5 used in the axial Chiral current formulas?

    ...the axial Chiral current formulas use the symbol J^5...i.e.,( "J" with a post script 5. ) What is the reason for the "5" ..??
  16. S

    A Exploring Chiral Symmetry in Weak Interaction

    Dear all Do we have chiral symmetry for weak interaction? I know that weak interaction is chiral. thank you
  17. Andrea M.

    Yang-Mills theory, confinement and chiral symmetry breaking

    I was thinking about hadrons in general Yang-Mills theory and I have some doubts that I'd like to discuss with you. Suppose that we have a Yang-Mills theory that, like QCD, tend to bind quarks into color singlet states. So far nothing strange, even QED tend to bind electromagnetic charges to...
  18. P

    Book says threonine has chiral center in its sidechain? How?

    Text says that threonine and isoleucine have a chiral carbon in sidechain. I am not seeing it. The carbon in the sidechain that is next to the alpha carbon is attached to an oxygen, a hydrogen, a carbon (a methyl group) and the alpha carbon. So that means its attached to two carbons, so...
  19. P

    Lorentz Transformation on Left & Right Chiral Spinors

    I will start with a summary of my confusion: I came across seemingly contradictory transformation rules for left and right chiral spinor in 2 books, and am unable to understand what part is Physics and what part is convention. Or is it that one of the two books incorrectly writes the...
  20. toforfiltum

    Exploring the Mystery of Sorbitol's 4 Chiral Centres

    I wonder why the number of chiral centres in sorrbital is 4? Why isn't it 2? Is it because the H-C-OH bond cannot be rotated? Otherwise isn't the two chiral centres above identical to the 2 at the bottom?
  21. Destroxia

    Second Chiral Center Mishap....?

    Homework Statement The Attempt at a Solution My issue here is the priority, I know OH has the greatest priority, and H the least, but I really cannot figure out the priority of the other 2 bonded to the carbon... ??
  22. Destroxia

    Chiral Center Priority: Determining R and S Configurations Using CIP Rules

    Homework Statement Say you have a chiral center carbon, attached to it are a H, a CH3, an OH, and a CH2CH2OH. The H is pointing away from you, and in a clockwise direction it goes, CH3, OH, CH2CH2OH My question is what is the priority of this? My main confusion is in the fact that since both...
  23. arivero

    Puzzling Chiral Symmetry Breaking

    Thinking aloud. Most descriptions of chiral symmetry breaking nowadays present it as something happening in QCD. But it was defined well before of the quark theory, and then it was something related to isospin symmetry. It is a bit puzzling because it seems as if pion mass were originated...
  24. S

    Why chiral fermions don't exist in odd dimensions?

    In four dimensions, left and right chiral fermion can be written as \psi_L= \begin{pmatrix} \psi_+\\ 0 \end{pmatrix},\qquad \psi_R= \begin{pmatrix} 0\\ \psi_- \end{pmatrix}, respectively, where \psi_+ and \psi_- are some two components spinors(Weyl spinors?). In this representation, the...
  25. ohwilleke

    Does Chiral EM Asymmetry Imply Matter-Antimatter Asymmetry?

    A Science Daily report discusses observations of cosmic gamma rays that suggest that magnetic fields in the universe disproportionately have left handed rather than right handed helicity. It goes on to suggest that under a 2001 theory of another physicist that this could explain...
  26. AdityaDev

    Alkylation of Imines: achiral to chiral compounds

    I found this in "March's Advanced organic chemistry" After that step, on using HCl in pentane, you will get 4-methyl-3-Heptanone. So this method was used to convert achiral 2-pentanone to a chiral compound, by first converting it to the compound on left by addition reaction and then using a 2...
  27. L

    Why complex reps of gauge group for chiral theory?

    Why must the gauge group be in a complex representation so that chirality of the fermions is respected? thanks
  28. quantatanu0

    Cut-off Regularization of Chiral Perturbation Theory

    I was trying to learn renormalization in the context of ChPT using momentum-space cut-off regularization procedure at one-loop order using order of p^2 Lagrangian. So, 1. There are counter terms in ChPT of order of p^4 when calculating in one-loop order using Lagrangian of order p^2 . 2...
  29. P

    Vector under Chiral transformation

    Was reading how do vectors transform under chiral transformation and found the following: If $$V^\mu$$ is a vector; set $$ V^\mu = \bar{\psi} \gamma^\mu \psi= $$ $$\bar{\psi}\gamma^\mu e^{-i\alpha\gamma^5}e^{i\alpha\gamma^5}\psi =$$ $$\bar{\psi}\gamma^\mu\psi = V^\mu $$ My questions are why...
  30. arivero

    Sum of spin for chiral particles?

    How does the spin of a pair of particles work if both particles are known to be chiral? generically if I sum the spins of two different (EDIT: spin 1/2, indeed ;-) particles I expect to get a triplet with S=1 \uparrow\uparrow, \uparrow\downarrow+\downarrow\uparrow, \downarrow\downarrow and...
  31. M

    Chiral gauge theory and C-symmetry

    Hi, I have a question in Srednicki's QFT textbook. In p.460 section 75(about Chiral gauge theory), it says "In spinor electrodynamics, the fact that the vector potential is odd under charge conjugation implies that the sum of these diagrams(exact 3photon vertex at one-loop) must vanish."...
  32. arivero

    Chiral leptoquarks and vector currents

    In a comment http://motls.blogspot.com.es/2014/07/cms-sees-650-gev-leptoquarks.html#comment-1479399237 to Motl's blog, there are some reference to "chiral leptoquarks". I am guessing that this is an object which is not a Dirac fermion, ie it only exists one of the two chiral components of it...
  33. ChrisVer

    Constraints on Chiral superfield

    Suppose we have a superfield \Phi(x,\theta,\bar{\theta}) this can be expanded in component fields in the standard way as: \Phi(x,\theta,\bar{\theta})= c(x) + \theta \psi(x) + \bar{\theta} \bar{ζ}(x) + \theta^{2} F(x) + \bar{\theta}^{2} Z(x) + \theta \sigma^{\mu} \bar{\theta} u_{\mu}(x) +...
  34. ChrisVer

    How Does Chiral Symmetry Breakdown Influence Meson Mass Differences?

    Why is the chiral symmetry breakdown determined for the vector/axial current as: V = \frac{m_{π^{+}}-m_{π^{0}}}{m_{π^{0}}+m_{π^{+}}}\approx 0.01 A= \frac{m_{π^{+}}-m_{f^{0}}}{m_{f^{0}}+m_{π^{+}}}\approx 1 ? why do we choose the difference between the pion+ (~140MeV) and pion0 (~135MeV)...
  35. J

    Chiral life concept - creating mirror image synthetic life?

    Imagine mirror image of a cell - built from a scratch using mirror images (enantiomers) of molecules of the original cell. It should work as standard one, but use e.g. L-sugars instead of our D-sugars: article. Some possible applications: - doubling the space of possible enzymes we could...
  36. N

    Finding Chiral Centres in Ring Structures

    How to find chiral centres of rings structures?For example take the following ringhttp://img203.imageshack.us/img203/7994/8vmq.jpg How to calculate no. of chiral centres?? thanks
  37. C

    Self energy logarithmic divergence due to chiral symmetry.

    In peskin at page 319 right above equation (10.6) he writes "If the constant term in a taylor expansion of the self energy were proportional to the cutoff ##\Lambda##, the electron mass shift would also have a term proportional to ##\Lambda##. But the electron mass shift must actually be...
  38. tsuwal

    Chemistry Chirality: why these molecules are not chiral?

    Homework Statement Look at the image please. The image shows 3 pairs of compounds. Explain why the first two are not chiral but the last one is chiral. Homework Equations Ar means Aromatic ring Aquirais means aquiral Quirais means chiral The Attempt at a Solution...
  39. J.Hong

    Operator algebra of chiral quasi-primary fields

    Studying conformal field theory, I tried to derive general expression for the commutation relations of the modes of two chiral quasi-primary fields. At first, I expressed the modes \phi_{(i)m} and \phi_{(j)n} as contour integrals over each fields, and took commutation relation. I used...
  40. C

    Relationship between photochemical mechanisms and chiral molecules

    I'm way outside my realm of knowledge here so perhaps I need some help polishing my question or the concepts behind it. Thank you for your patience. Does the orientation of circularly polarized light (CPL) as a reaction mechanism influence the chirality of the molecule in a general manner...
  41. Einj

    Chiral symmetry and quark condensate

    I'm studying chiral symmetry in QCD. I understand that in order for a spontaneous symmetry breaking to occur, there must be some state with a vacuum expectation value different from zero. My question is: can someone prove that is the chiral symmetry is an exact symmetry of the QCD then...
  42. Hepth

    Chiral Perturbation Theory : pi0 pi0 Z vertex?

    Not sure if anyone has any experience with chiral perturbation theory, but I'm trying to see what all of the vertices are for interactions with a single Z boson. I've looked at the lagrangian up to order p^4 so far, and it seems that the Z only interacts with charged pions/kaons. I'm using...
  43. A

    Achiral and Chiral Compounds - B and D

    Compounds B and D both have no chiralaty centers - but it seems to me that B has a plane of symmetry so it's achiral, and D has no plane of symmetry so it's chiral. I always thought though, that if a compound has no chiral centers then you can say with conffidence it's achiral. Is my analysis...
  44. R

    2 dimensional chiral boson theory

    I am reading the paper "Covariant Action for a D=11 Five-Brane with the Chiral Field" and want to make an analog for the chiral field in 2 dimensions. But I don't know at the starting point, for if I take the local coordinates of the worldvolume to be ##x^m (m=0,1)##, the dual field strength...
  45. AGNuke

    Choose from Unknown - A Chiral Compound

    A C8H12 chiral hydrocarbon, X, is reduced by catalytic Hydrogenation to an achiral C8H14. Ozonolysis (Oxidative) of X gave a chiral C8H12O4 dicarboxylic acid. Choose X from the given. Attempt I first determined the chirality of the given alternatives. That rules out the 2nd option, as it...
  46. O

    Pyrrolidine: Achiral or chiral?

    Hi everyone, this is my first time posting to this website. I'm just trying to study for organic chemistry, and I've been having a little trouble trying to grasp the concept of chiral/achiral. The book talks about pyrrolidine,C4H9N, and it asks whether or not pyrrolidine could be used to...
  47. H

    I don't understand why it's chiral. It's not like any of the phenyl

    I don't understand why it's chiral. It's not like any of the phenyl rings are stuck in a single resonance structure.
  48. Hepth

    Chiral Perturbation Theory : Some quick questions

    I just want to make sure that I am doing some things correctly. I'll be using http://www.physics.umd.edu/courses/Phys741/xji/chapter5.pdf from about 5.64 on. The kinetic term : \frac{f^2}{4} Tr[D_{\mu} \Sigma D^{\mu} \Sigma^{\dagger}] Now if I want to expand this out, as \Sigma =e^{i...
  49. M

    Understanding Chirality and Enantiomers: Differences and Similarities

    What makes something chiral, but not an enantiomer? It seems like they have the exact same definition
  50. P

    Oxidation state and chiral configurations

    I'm doing this same problem found on the following link for a biochemistry homework. http://www.chegg.com/homework-help/questions-and-answers/nucleoside-phosphorothioates-synthetic-nucleotide-analogs-used-enzymology-molecular-biolog-q1481931 My question is regarding both finding the...