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73-562: For biological macromolecules and cell organelles like ribosomes , the sedimentation rate is typically measured as the rate of travel in a centrifuge tube subjected to high g-force . The svedberg (S) is distinct from the SI unit sievert or the non-SI unit sverdrup , which also use the symbol Sv, and to the SI unit Siemens which uses the symbol S too. The unit is named after the Swedish chemist Theodor Svedberg (1884–1971), winner of

146-403: A trans isomer where the two chlorines are on the same plane as the two carbons, but with oppositely directed bonds; and two gauche isomers, mirror images of each other, where the two − CH 2 Cl {\displaystyle {\ce {-CH2Cl}}} groups are rotated about 109° from that position. The computed energy difference between trans and gauche

219-399: A "parent" molecule (propane, in that case). There are also three structural isomers of the hydrocarbon C 3 H 4 {\displaystyle {\ce {C3H4}}} : In two of the isomers, the three carbon atoms are connected in an open chain, but in one of them ( propadiene or allene; I ) the carbons are connected by two double bonds , while in

292-516: A branched structure of multiple phenolic subunits. They can perform structural roles (e.g. lignin ) as well as roles as secondary metabolites involved in signalling , pigmentation and defense . Some examples of macromolecules are synthetic polymers ( plastics , synthetic fibers , and synthetic rubber ), graphene , and carbon nanotubes . Polymers may be prepared from inorganic matter as well as for instance in inorganic polymers and geopolymers . The incorporation of inorganic elements enables

365-473: A chain of three carbon atoms connected by single bonds, with the remaining carbon valences being filled by seven hydrogen atoms and by a hydroxyl group − OH {\displaystyle {\ce {-OH}}} comprising the oxygen atom bound to a hydrogen atom. These two isomers differ on which carbon the hydroxyl is bound to: either to an extremity of the carbon chain propan-1-ol (1-propanol, n -propyl alcohol, n -propanol; I ) or to

438-554: A conformation isomer is separated from any other isomer by an energy barrier : the amount that must be temporarily added to the internal energy of the molecule in order to go through all the intermediate conformations along the "easiest" path (the one that minimizes that amount). A classic example of conformational isomerism is cyclohexane . Alkanes generally have minimum energy when the C − C − C {\displaystyle {\ce {C-C-C}}} angles are close to 110 degrees. Conformations of

511-469: A large part of the volume of the solution, thereby increasing the effective concentrations of these molecules. All living organisms are dependent on three essential biopolymers for their biological functions: DNA , RNA and proteins . Each of these molecules is required for life since each plays a distinct, indispensable role in the cell . The simple summary is that DNA makes RNA, and then RNA makes proteins . DNA, RNA, and proteins all consist of

584-428: A left hand and a right hand. The two shapes are said to be chiral . A classical example is bromochlorofluoromethane ( CHFClBr {\displaystyle {\ce {CHFClBr}}} ). The two enantiomers can be distinguished, for example, by whether the path F ⟶ Cl ⟶ Br {\displaystyle {\ce {F->Cl->Br}}} turns clockwise or counterclockwise as seen from

657-428: A molecule that are connected by just one single bond can rotate about that bond. While the bond itself is indifferent to that rotation, attractions and repulsions between the atoms in the two parts normally cause the energy of the whole molecule to vary (and possibly also the two parts to deform) depending on the relative angle of rotation φ between the two parts. Then there will be one or more special values of φ for which

730-547: A molecule. Therefore, the possible isomers of a compound in solution or in its liquid and solid phases many be very different from those of an isolated molecule in vacuum. Even in the gas phase, some compounds like acetic acid will exist mostly in the form of dimers or larger groups of molecules, whose configurations may be different from those of the isolated molecule. Two compounds are said to be enantiomers if their molecules are mirror images of each other, that cannot be made to coincide only by rotations or translations – like

803-510: A much greater stability against breakdown than does RNA, an attribute primarily associated with the absence of the 2'-hydroxyl group within every nucleotide of DNA. Third, highly sophisticated DNA surveillance and repair systems are present which monitor damage to the DNA and repair the sequence when necessary. Analogous systems have not evolved for repairing damaged RNA molecules. Consequently, chromosomes can contain many billions of atoms, arranged in

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876-423: A real compound; they are fictions devised as a way to describe (by their "averaging" or "resonance") the actual delocalized bonding of o -xylene, which is the single isomer of C 8 H 10 {\displaystyle {\ce {C8H10}}} with a benzene core and two methyl groups in adjacent positions. Stereoisomers have the same atoms or isotopes connected by bonds of

949-402: A repeating structure of related building blocks ( nucleotides in the case of DNA and RNA, amino acids in the case of proteins). In general, they are all unbranched polymers, and so can be represented in the form of a string. Indeed, they can be viewed as a string of beads, with each bead representing a single nucleotide or amino acid monomer linked together through covalent chemical bonds into

1022-638: A single isomer, depending on the temperature and the context. For example, the two conformations of cyclohexane convert to each other quite rapidly at room temperature (in the liquid state), so that they are usually treated as a single isomer in chemistry. In some cases, the barrier can be crossed by quantum tunneling of the atoms themselves. This last phenomenon prevents the separation of stereoisomers of fluorochloroamine NHFCl {\displaystyle {\ce {NHFCl}}} or hydrogen peroxide H 2 O 2 {\displaystyle {\ce {H2O2}}} , because

1095-409: A single molecule. For example, a single polymeric molecule is appropriately described as a "macromolecule" or "polymer molecule" rather than a "polymer," which suggests a substance composed of macromolecules. Because of their size, macromolecules are not conveniently described in terms of stoichiometry alone. The structure of simple macromolecules, such as homopolymers, may be described in terms of

1168-427: A specific chemical structure. Proteins are functional macromolecules responsible for catalysing the biochemical reactions that sustain life. Proteins carry out all functions of an organism, for example photosynthesis, neural function, vision, and movement. The single-stranded nature of protein molecules, together with their composition of 20 or more different amino acid building blocks, allows them to fold in to

1241-411: A specified protein. On the other hand, the sequence information of a protein molecule is not used by cells to functionally encode genetic information. DNA has three primary attributes that allow it to be far better than RNA at encoding genetic information. First, it is normally double-stranded, so that there are a minimum of two copies of the information encoding each gene in every cell. Second, DNA has

1314-459: A vast number of different three-dimensional shapes, while providing binding pockets through which they can specifically interact with all manner of molecules. In addition, the chemical diversity of the different amino acids, together with different chemical environments afforded by local 3D structure, enables many proteins to act as enzymes , catalyzing a wide range of specific biochemical transformations within cells. In addition, proteins have evolved

1387-1131: A very large number of three-dimensional structures. Some of these structures provide binding sites for other molecules and chemically active centers that can catalyze specific chemical reactions on those bound molecules. The limited number of different building blocks of RNA (4 nucleotides vs >20 amino acids in proteins), together with their lack of chemical diversity, results in catalytic RNA ( ribozymes ) being generally less-effective catalysts than proteins for most biological reactions. The Major Macromolecules: (Polymer) (Monomer) Carbohydrate macromolecules ( polysaccharides ) are formed from polymers of monosaccharides . Because monosaccharides have multiple functional groups , polysaccharides can form linear polymers (e.g. cellulose ) or complex branched structures (e.g. glycogen ). Polysaccharides perform numerous roles in living organisms, acting as energy stores (e.g. starch ) and as structural components (e.g. chitin in arthropods and fungi). Many carbohydrates contain modified monosaccharide units that have had functional groups replaced or removed. Polyphenols consist of

1460-442: A very long chain. In most cases, the monomers within the chain have a strong propensity to interact with other amino acids or nucleotides. In DNA and RNA, this can take the form of Watson–Crick base pairs (G–C and A–T or A–U), although many more complicated interactions can and do occur. Because of the double-stranded nature of DNA, essentially all of the nucleotides take the form of Watson–Crick base pairs between nucleotides on

1533-631: Is a very large molecule important to biological processes , such as a protein or nucleic acid . It is composed of thousands of covalently bonded atoms . Many macromolecules are polymers of smaller molecules called monomers . The most common macromolecules in biochemistry are biopolymers ( nucleic acids , proteins , and carbohydrates ) and large non-polymeric molecules such as lipids , nanogels and macrocycles . Synthetic fibers and experimental materials such as carbon nanotubes are also examples of macromolecules. Macromolecule Large molecule A molecule of high relative molecular mass,

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1606-461: Is not another isomer, since the difference between it and 1-propanol is not real; it is only the result of an arbitrary choice in the direction of numbering the carbons along the chain. For the same reason, "ethoxymethane" is the same molecule as methoxyethane, not another isomer. 1-Propanol and 2-propanol are examples of positional isomers , which differ by the position at which certain features, such as double bonds or functional groups , occur on

1679-440: Is not chiral: the mirror image of its molecule is also obtained by a half-turn about a suitable axis. Another example of a chiral compound is 2,3-pentadiene H 3 C − CH = C = CH − CH 3 {\displaystyle {\ce {H3C-CH=C=CH-CH3}}} a hydrocarbon that contains two overlapping double bonds. The double bonds are such that

1752-565: Is on "this side" or "the other side" of the ring's mean plane. Discounting isomers that are equivalent under rotations, there are nine isomers that differ by this criterion, and behave as different stable substances (two of them being enantiomers of each other). The most common one in nature ( myo -inositol) has the hydroxyls on carbons 1, 2, 3 and 5 on the same side of that plane, and can therefore be called cis -1,2,3,5- trans -4,6-cyclohexanehexol. And each of these cis - trans isomers can possibly have stable "chair" or "boat" conformations (although

1825-435: Is rather low (~8 kJ /mol). This steric hindrance effect is more pronounced when those four hydrogens are replaced by larger atoms or groups, like chlorines or carboxyls . If the barrier is high enough for the two rotamers to be separated as stable compounds at room temperature, they are called atropisomers . Large molecules may have isomers that differ by the topology of their overall arrangement in space, even if there

1898-604: Is restricted by a somewhat rigid framework of other atoms. For example, in the cyclic alcohol inositol ( CHOH ) 6 {\displaystyle {\ce {(CHOH)6}}} (a six-fold alcohol of cyclohexane), the six-carbon cyclic backbone largely prevents the hydroxyl − OH {\displaystyle {\ce {-OH}}} and the hydrogen − H {\displaystyle {\ce {-H}}} on each carbon from switching places. Therefore, one has different configurational isomers depending on whether each hydroxyl

1971-477: Is the angular velocity in radians per second. Bigger particles tend to sediment faster and so have higher Svedberg values. Svedberg units are not directly additive since they represent a rate of sedimentation, not weight. In centrifugation of small biochemical species, a convention has developed in which sedimentation coefficients are expressed in the Svedberg units. Macromolecule A macromolecule

2044-455: Is the ether methoxyethane (ethyl-methyl-ether; III ). Unlike the other two, it has the oxygen atom connected to two carbons, and all eight hydrogens bonded directly to carbons. It can be described by the condensed formula H 3 C − CH 2 − O − CH 3 {\displaystyle {\ce {H3C-CH2-O-CH3}}} . The alcohol "3-propanol"

2117-416: Is the ratio of the speed of a substance in a centrifuge to its acceleration in comparable units. A substance with a sedimentation coefficient of 26S ( 26 × 10 s ) will travel at 26 micrometers per second ( 26 × 10 m/s ) under the influence of an acceleration of a million gravities (10 m/s). Centrifugal acceleration is given as rω ; where r is the radial distance from the rotation axis and ω

2190-531: Is their relative insolubility in water and similar solvents , instead forming colloids . Many require salts or particular ions to dissolve in water. Similarly, many proteins will denature if the solute concentration of their solution is too high or too low. High concentrations of macromolecules in a solution can alter the rates and equilibrium constants of the reactions of other macromolecules, through an effect known as macromolecular crowding . This comes from macromolecules excluding other molecules from

2263-426: Is true if a center with six or more equivalent bonds has two or more substituents. For instance, in the compound PF 4 Cl {\displaystyle {\ce {PF4Cl}}} , the bonds from the phosphorus atom to the five halogens have approximately trigonal bipyramidal geometry . Thus two stereoisomers with that formula are possible, depending on whether the chlorine atom occupies one of

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2336-412: Is ~1.5 kcal/mol, the barrier for the ~109° rotation from trans to gauche is ~5 kcal/mol, and that of the ~142° rotation from one gauche to its enantiomer is ~8 kcal/mol. The situation for butane is similar, but with sightly lower gauche energies and barriers. If the two parts of the molecule connected by a single bond are bulky or charged, the energy barriers may be much higher. For example, in

2409-462: The C − C {\displaystyle {\ce {C-C}}} axis. Thus, even if those angles and distances are assumed fixed, there are infinitely many conformations for the ethane molecule, that differ by the relative angle φ of rotation between the two groups. The feeble repulsion between the hydrogen atoms in the two methyl groups causes the energy to minimized for three specific values of φ, 120° apart. In those configurations,

2482-479: The cis and trans labels are ambiguous. The IUPAC recommends a more precise labeling scheme, based on the CIP priorities for the bonds at each carbon atom. More generally, atoms or atom groups that can form three or more non-equivalent single bonds (such as the transition metals in coordination compounds) may give rise to multiple stereoisomers when different atoms or groups are attached at those positions. The same

2555-428: The 1920s, although his first relevant publication on this field only mentions high molecular compounds (in excess of 1,000 atoms). At that time the term polymer , as introduced by Berzelius in 1832, had a different meaning from that of today: it simply was another form of isomerism for example with benzene and acetylene and had little to do with size. Usage of the term to describe large molecules varies among

2628-427: The 1926 Nobel Prize in chemistry for his work on disperse systems, colloids and his invention of the ultracentrifuge . The Svedberg coefficient is a nonlinear function. A particle's mass, density, and shape will determine its S value. The S value depends on the frictional forces retarding its movement, which, in turn, are related to the average cross-sectional area of the particle. The sedimentation coefficient

2701-460: The ability to bind a wide range of cofactors and coenzymes , smaller molecules that can endow the protein with specific activities beyond those associated with the polypeptide chain alone. RNA is multifunctional, its primary function is to encode proteins , according to the instructions within a cell's DNA. They control and regulate many aspects of protein synthesis in eukaryotes . RNA encodes genetic information that can be translated into

2774-426: The ability to catalyse biochemical reactions. DNA is an information storage macromolecule that encodes the complete set of instructions (the genome ) that are required to assemble, maintain, and reproduce every living organism. DNA and RNA are both capable of encoding genetic information, because there are biochemical mechanisms which read the information coded within a DNA or RNA sequence and use it to generate

2847-493: The amino acid sequence of proteins, as evidenced by the messenger RNA molecules present within every cell, and the RNA genomes of a large number of viruses. The single-stranded nature of RNA, together with tendency for rapid breakdown and a lack of repair systems means that RNA is not so well suited for the long-term storage of genetic information as is DNA. In addition, RNA is a single-stranded polymer that can, like proteins, fold into

2920-457: The atoms back to the original positions. Changing the shape of the molecule from such an energy minimum A {\displaystyle {\ce {A}}} to another energy minimum B {\displaystyle {\ce {B}}} will therefore require going through configurations that have higher energy than A {\displaystyle {\ce {A}}} and B {\displaystyle {\ce {B}}} . That is,

2993-470: The atoms differ; and stereoisomerism or (spatial isomerism), in which the bonds are the same but the relative positions of the atoms differ. Isomeric relationships form a hierarchy . Two chemicals might be the same constitutional isomer, but upon deeper analysis be stereoisomers of each other. Two molecules that are the same stereoisomer as each other might be in different conformational forms or be different isotopologues . The depth of analysis depends on

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3066-495: The barriers between these are significantly lower than those between different cis - trans isomers). Cis and trans isomers also occur in inorganic coordination compounds , such as square planar MX 2 Y 2 {\displaystyle {\ce {MX2Y2}}} complexes and octahedral MX 4 Y 2 {\displaystyle {\ce {MX4Y2}}} complexes. For more complex organic molecules,

3139-426: The carbons alternately above and below their mean plane) and boat (with two opposite carbons above the plane, and the other four below it). If the energy barrier between two conformational isomers is low enough, it may be overcome by the random inputs of thermal energy that the molecule gets from interactions with the environment or from its own vibrations . In that case, the two isomers may as well be considered

3212-413: The case of certain macromolecules for which the properties may be critically dependent on fine details of the molecular structure. 2. If a part or the whole of the molecule fits into this definition, it may be described as either macromolecular or polymeric , or by polymer used adjectivally. The term macromolecule ( macro- + molecule ) was coined by Nobel laureate Hermann Staudinger in

3285-460: The central atom M forms six bonds with octahedral geometry , has at least two facial–meridional isomers , depending on whether the three X {\displaystyle {\ce {X}}} bonds (and thus also the three Y {\displaystyle {\ce {Y}}} bonds) are directed at the three corners of one face of the octahedron ( fac isomer), or lie on the same equatorial or "meridian" plane of it ( mer isomer). Two parts of

3358-460: The compound biphenyl – two phenyl groups connected by a single bond – the repulsion between hydrogen atoms closest to the central single bond gives the fully planar conformation, with the two rings on the same plane, a higher energy than conformations where the two rings are skewed. In the gas phase, the molecule has therefore at least two rotamers, with the ring planes twisted by ±47°, which are mirror images of each other. The barrier between them

3431-433: The cyclohexane molecule with all six carbon atoms on the same plane have a higher energy, because some or all the C − C − C {\displaystyle {\ce {C-C-C}}} angles must be far from that value (120 degrees for a regular hexagon). Thus the conformations which are local energy minima have the ring twisted in space, according to one of two patterns known as chair (with

3504-421: The disciplines. For example, while biology refers to macromolecules as the four large molecules comprising living things, in chemistry , the term may refer to aggregates of two or more molecules held together by intermolecular forces rather than covalent bonds but which do not readily dissociate. According to the standard IUPAC definition, the term macromolecule as used in polymer science refers only to

3577-426: The energy is at a local minimum. The corresponding conformations of the molecule are called rotational isomers or rotamers . Thus, for example, in an ethane molecule H 3 C − CH 3 {\displaystyle {\ce {H3C-CH3}}} , all the bond angles and length are narrowly constrained, except that the two methyl groups can independently rotate about

3650-406: The equilibrium between neutral and zwitterionic forms of an amino acid . The structure of some molecules is sometimes described as a resonance between several apparently different structural isomers. The classical example is 1,2-dimethylbenzene ( o -xylene), which is often described as a mix of the two apparently distinct structural isomers: However, neither of these two structures describes

3723-442: The field of study or the chemical and physical properties of interest. The English word "isomer" ( / ˈ aɪ s əm ər / ) is a back-formation from "isomeric", which was borrowed through German isomerisch from Swedish isomerisk ; which in turn was coined from Greek ἰσόμερoς isómeros , with roots isos = "equal", méros = "part". Structural isomers have the same number of atoms of each element (hence

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3796-564: The hydrogen atom. In order to change one conformation to the other, at some point those four atoms would have to lie on the same plane – which would require severely straining or breaking their bonds to the carbon atom. The corresponding energy barrier between the two conformations is so high that there is practically no conversion between them at room temperature, and they can be regarded as different configurations. The compound chlorofluoromethane CH 2 ClF {\displaystyle {\ce {CH2ClF}}} , in contrast,

3869-486: The individual monomer subunit and total molecular mass . Complicated biomacromolecules, on the other hand, require multi-faceted structural description such as the hierarchy of structures used to describe proteins . In British English , the word "macromolecule" tends to be called " high polymer ". Macromolecules often have unusual physical properties that do not occur for smaller molecules. Another common macromolecular property that does not characterize smaller molecules

3942-462: The internal energy of a molecule, which is determined by the angles between bonds in each atom and by the distances between atoms (whether they are bonded or not). A conformational isomer is an arrangement of the atoms of the molecule or ion for which the internal energy is a local minimum ; that is, an arrangement such that any small changes in the positions of the atoms will increase the internal energy, and hence result in forces that tend to push

4015-638: The middle carbon propan-2-ol (2-propanol, isopropyl alcohol, isopropanol; II ). These can be described by the condensed structural formulas H 3 C − CH 2 − CH 2 OH {\displaystyle {\ce {H3C-CH2-CH2OH}}} and H 3 C − CH ( OH ) − CH 3 {\displaystyle {\ce {H3C-CH(OH)-CH3}}} . The third isomer of C 3 H 8 O {\displaystyle {\ce {C3H8O}}}

4088-585: The molecule 1,2-dichloroethane ( ClH 2 C − CH 2 Cl {\displaystyle {\ce {ClH2C-CH2Cl}}} also has three local energy minima, but they have different energies due to differences between the H − H {\displaystyle {\ce {H-H}}} , Cl − Cl {\displaystyle {\ce {Cl-Cl}}} , and H − Cl {\displaystyle {\ce {H-Cl}}} interactions. There are therefore three rotamers:

4161-410: The molecule, not just two different conformations. (However, one should be aware that the terms "conformation" and "configuration" are largely synonymous outside of chemistry, and their distinction may be controversial even among chemists. ) Interactions with other molecules of the same or different compounds (for example, through hydrogen bonds ) can significantly change the energy of conformations of

4234-408: The other ( propyne or methylacetylene; II ) they are connected by a single bond and a triple bond . In the third isomer ( cyclopropene ; III ) the three carbons are connected into a ring by two single bonds and a double bond. In all three, the remaining valences of the carbon atoms are satisfied by the four hydrogens. Again, note that there is only one structural isomer with a triple bond, because

4307-654: The other possible placement of that bond is just drawing the three carbons in a different order. For the same reason, there is only one cyclopropene, not three. Tautomers are structural isomers which readily interconvert, so that two or more species co-exist in equilibrium such as H − X − Y = Z ↽ − − ⇀ X = Y − Z − H {\displaystyle {\ce {H-X-Y=Z <=> X=Y-Z-H}}} . Important examples are keto-enol tautomerism and

4380-514: The other side of"), respectively; or Z and E in the IUPAC recommended nomenclature. Conversion between these two forms usually requires temporarily breaking bonds (or turning the double bond into a single bond), so the two are considered different configurations of the molecule. More generally, cis – trans isomerism (formerly called "geometric isomerism") occurs in molecules where the relative orientation of two distinguishable functional groups

4453-819: The plane of polarized light that passes through it. The rotation has the same magnitude but opposite senses for the two isomers, and can be a useful way of distinguishing and measuring their concentration in a solution. For this reason, enantiomers were formerly called "optical isomers". However, this term is ambiguous and is discouraged by the IUPAC . Stereoisomers that are not enantiomers are called diastereomers . Some diastereomers may contain chiral center , some not. Some enantiomer pairs (such as those of trans -cyclooctene ) can be interconverted by internal motions that change bond lengths and angles only slightly. Other pairs (such as CHFClBr) cannot be interconverted without breaking bonds, and therefore are different configurations. A double bond between two carbon atoms forces

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4526-423: The presence of chiral catalysts , such as most enzymes . For this latter reason, the two enantiomers of most chiral compounds usually have markedly different effects and roles in living organisms. In biochemistry and food science , the two enantiomers of a chiral molecule – such as glucose – are usually identified, and treated as very different substances. Each enantiomer of a chiral compound typically rotates

4599-529: The remaining four bonds (if they are single) to lie on the same plane, perpendicular to the plane of the bond as defined by its π orbital . If the two bonds on each carbon connect to different atoms, two distinct conformations are possible, that differ from each other by a twist of 180 degrees of one of the carbons about the double bond. The classical example is dichloroethene C 2 H 2 Cl 2 {\displaystyle {\ce {C2H2Cl2}}} , specifically

4672-481: The same molecular formula ), but the atoms are connected in distinct ways. For example, there are three distinct compounds with the molecular formula C 3 H 8 O {\displaystyle {\ce {C3H8O}}} : The first two isomers shown of C 3 H 8 O {\displaystyle {\ce {C3H8O}}} are propanols , that is, alcohols derived from propane . Both have

4745-409: The same type, but differ in their shapes – the relative positions of those atoms in space – apart from rotations and translations . In theory, one can imagine any arrangement in space of the atoms of a molecule or ion to be gradually changed to any other arrangement in infinitely many ways, by moving each atom along an appropriate path. However, changes in the positions of atoms will generally change

4818-406: The six planes H − C − C {\displaystyle {\ce {H-C-C}}} or C − C − H {\displaystyle {\ce {C-C-H}}} are 60° apart. Discounting rotations of the whole molecule, that configuration is a single isomer – the so-called staggered conformation. Rotation between the two halves of

4891-412: The structural isomer Cl − HC = CH − Cl {\displaystyle {\ce {Cl-HC=CH-Cl}}} that has one chlorine bonded to each carbon. It has two conformational isomers, with the two chlorines on the same side or on opposite sides of the double bond's plane. They are traditionally called cis (from Latin meaning "on this side of") and trans ("on

4964-425: The structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass. 1. In many cases, especially for synthetic polymers, a molecule can be regarded as having a high relative molecular mass if the addition or removal of one or a few of the units has a negligible effect on the molecular properties. This statement fails in

5037-460: The three middle carbons are in a straight line, while the first three and last three lie on perpendicular planes. The molecule and its mirror image are not superimposable, even though the molecule has an axis of symmetry. The two enantiomers can be distinguished, for example, by the right-hand rule . This type of isomerism is called axial isomerism . Enantiomers behave identically in chemical reactions, except when reacted with chiral compounds or in

5110-575: The tunability of properties and/or responsive behavior as for instance in smart inorganic polymers . Isomerism In chemistry , isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism refers to the existence or possibility of isomers. Isomers do not necessarily share similar chemical or physical properties . Two main forms of isomerism are structural (or constitutional) isomerism, in which bonds between

5183-448: The two "axial" positions, or one of the three "equatorial" positions. For the compound PF 3 Cl 2 {\displaystyle {\ce {PF3Cl2}}} , three isomers are possible, with zero, one, or two chlorines in the axial positions. As another example, a complex with a formula like MX 3 Y 3 {\displaystyle {\ce {MX3Y3}}} , where

5256-438: The two complementary strands of the double helix . In contrast, both RNA and proteins are normally single-stranded. Therefore, they are not constrained by the regular geometry of the DNA double helix, and so fold into complex three-dimensional shapes dependent on their sequence. These different shapes are responsible for many of the common properties of RNA and proteins, including the formation of specific binding pockets , and

5329-484: The two conformations with minimum energy interconvert in a few picoseconds even at very low temperatures. Conversely, the energy barrier may be so high that the easiest way to overcome it would require temporarily breaking and then reforming one or more bonds of the molecule. In that case, the two isomers usually are stable enough to be isolated and treated as distinct substances. These isomers are then said to be different configurational isomers or "configurations" of

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