1 Define isomer and give examples.
2.What is an enantiomer? Why does the body manipulate and synthesize only one type of enantiomer?
- 1 decade agoFavorite Answer
1. Isomers (plural) aer compunds that have identical molecular formulas but differ in the ways in which the atoms are bonded together. There are 2 different kinds of isomers Constitutional isomers, which differ in the order and the way in which the atoms are bonded together in their molecules (i.e. the atoms have different connectivities). There are also stereoisomers, these molecules have the same connectivities and differ only in the arrangement of their atoms in space.
For example, butane, a 4 carbon molecule, can be arranged like so CH3CH2CH2CH3, or the 4 carbon molecule can be arranged like: CH3CH(CH3)CH3- in this molecule there are 3 carbon molecules bound in a line and the fourth carbon atom, instead of being attached in a straight line like in the previous exaple, is connected to the center of the 3 carbon atoms, consequently, this molecule is named 2-methylpropane.
Butane and 2-methyl isopropyl are constitutional isomers of each other; they have the same moecular formula but different structural formulas; their structures differ in connectivity. In butane, each C atom is attached to only 2 other carbon atoms, in 2-methylpropane, the center carbon atom is attached to 3 carbon atoms. Due to the difference in connectivity between these molecules, the compounds have different physical characteristics, such as different boiling points.
Similarily, the molecular formula C2H6O gives rise to 2 different connectivities: CH3CH2-OH (ethanol) and CH3-O-CH3 (dimethyl ether). There is a much larger difference between the boiling points of these two isomers as compared to that of the isomers butane and 2-methylpropane. This is due to the presence of carbon-oxygen bonds in the latter versus only carbon-hydrogen bonds in the former.
It is important to note that as the number of carbon atoms in a given molecule increase, the number of possible isomers for that molecule is greatly increased. For example, the molecular formula C3H60 can form 9 constitutional isomers.
2. In order to understand what an enantiomer is, one mjst understand what stereoisomers are. Stereoisomers have the same connectivity and differ from each other only in the way their atoms are oriented in space. Stereoisomerism is really just a more subtle form of isomerism. Stereoisomers cannot, howeverm be distinguished from each other by looking at their condensed structural formuals, which are identical.
A type of steroisomerism is called configurational isomerism. Configurational isomers differ from each other only in the arangement of their atoms in space and connot be converted from one into another by rotations about single bonds within molecules. Configurational isomers can be either enantiomers or diastereomers.
Enantiomers are stereoisomers that are mirror images if one another. All stereoisomers that are not enantiomers are diastereoisomers. Hypothetically, if you held up a mirror to a molecule, a mirror image may be drawn of any molecular structure. Isomerism exists only when mirror images are not superimposable on each other.
For example, Struture A (image in mirror) cannot be picked up and placed over Structure B, which is creating the image of structure A. No matter how the two molecules are rotated in space, the two structures will never get all of their point to coincide.
Stereoisomers that are non-superimposable mirror images of each other are caled enantiomers. A very way to understand the concept of enantiomers is hoding the palms of your hands so they are facing the ceiling. No matter how you move your hands, you will never be able to get them to superimpose on each other. This is called CHIRALITY.
An example of molecules that exist as an enantiomers are(+)-2-chlorobutane and (-)-2-chlorobutane. These two molecules cannot be superimposed on one, or the others, mirror image, and thus they are chiral molecules. Many compounds that occur in living organisms, such as carb's and proteins are chiral. In (+)-2-chlorobutane and (-)-2-clorobutane there exists a center carbon atom that has 4 different substituents attached to it. Although the substituents are the same, some atoms may be facing "out of the page" whilr others are facing "in the page."
Enantiomers have identical physical properties, with ONE EXECPTIION, they rotate plane-polarized light in opposite directions. Compounds that are able to rotate the plane of polarize light are said to have optical activity, or to be optically active. The plus and minus signs of 2-chlorobutane indicate which direction each molecule is capable of rotating light. A (-) suffix indicates counterclockwise rotation of plane polarized light, and (+) indicated clockwise rotation. Besides this property, all other physical proprties between enantiomers are identical. Therefore, they cannot be separated by physical means such as distillation or crystallization. Enantiomers are a type of configurational isomer.
The body only manipulates and syntheszies chiral molecules, or chiral enantiomers: molecules or any other object that cannot be sperimposed on itself. Carbohydrtes, proteins, and even human beings as a whole are chiral: internal organs are arranged assymmetrically, and we have distictive twists and whorls in the ways our hair grows. Our right and our left hands are nonsuperimposable mirror images of each other. (The word chiral actually comes from the Greek word hand).
The chirality of the human body, which is reflected at the most fundamental level in the sterochemsitry of enzyme systems, requires that chemical reactions take place with a particualr orientation in space. Thus, ine enantiomer of a hormone may be active, fitting correctly into the active site of the enzyme, while it's mirror image will not fit into the enzyme and will be completely inactive. Enantiomers have similar chemical properties when they are in achiral environments, however, when in chiral environments, such as the human body, the (+) and (-) enantiomers have very different chenical and physical properties. The biological system is extremely senstive to these differences in stereochemistry, and this is the reason that the body produces only one type of enantiomer, the chiral form.
Sorry this is so long; I was actually just studying this, so I may have written a bit too much. I hope this answers your questions though!Source(s): Organic Chemistry- Structure and Reactivity. Seyhan Ege
- 1 decade ago
1 different organization of the atoms in a molecule... im sure you can think of some
2 a carbon atom w/ 4 different groups off it and its mirror image are enantiomers.. anything without a plane of symmetry is. all the molecules in the body work together like enzymes and substrates, so they all have to be in a certain orientation to work together.Source(s): orgo exam last week!