Worked Example 5.1 Drawing the Three Dimensional Structure of a Chiral Molecule Strategy An alcohol is a compound that contains the-OH functional group To make an alcohol chiral,we need to have four different groups bonded to a single carbon atom,say-H,-OH,- CH3,and -CH2CH3
Strategy ▪ An alcohol is a compound that contains the –OH functional group ▪ To make an alcohol chiral, we need to have four different groups bonded to a single carbon atom, say –H, –OH, – CH3 , and –CH2CH3 Worked Example 5.1 Drawing the Three Dimensional Structure of a Chiral Molecule
Worked Example 5.1 Drawing the Three Dimensional Structure of a Chiral Molecule Solution OH CH3CH2-C* Butan-2-ol CH3 (chiral) H
Solution Worked Example 5.1 Drawing the Three Dimensional Structure of a Chiral Molecule
5.3 Optical Activity Stereochemistry Study originated in the early 19th century during the investigations by the French physicist Jean-Baptiste Biot into the nature of plane-polarized light A beam of ordinary light consists of electromagnetic waves that oscillate in an infinite number of planes at right angles to the direction of light travel When a beam of ordinary light passes through a device called a polarizer only light waves oscillating in a single plane pass through and the light is plane-polarized Optically active organic substances Biot observed that when a beam of plane-polarized light passes through a solution of certain organic molecules, the plane of polarization is rotated
Stereochemistry ▪ Study originated in the early 19th century during the investigations by the French physicist Jean-Baptiste Biot into the nature of plane-polarized light ▪ A beam of ordinary light consists of electromagnetic waves that oscillate in an infinite number of planes at right angles to the direction of light travel ▪ When a beam of ordinary light passes through a device called a polarizer only light waves oscillating in a single plane pass through and the light is plane-polarized Optically active organic substances ▪ Biot observed that when a beam of plane-polarized light passes through a solution of certain organic molecules, the plane of polarization is rotated 5.3 Optical Activity
Optical Activity Polarimeter Measures the amount (angle)of rotation A solution of optically active organic molecules is placed in a sample tube Plane-polarized light is passed through the tube Rotation of the polarization plane occurs Light goes through a second polarizer called the analyzer The new plane of polarization and degree of rotation can be found by rotating the analyzer until the light passes through it Angle of rotation is denoted a and is expressed in degrees Unpolarized light Polarized light Light Polarizer source Sample tube containing Analyzer organic molecules
Polarimeter ▪ Measures the amount (angle) of rotation ▪ A solution of optically active organic molecules is placed in a sample tube ▪ Plane-polarized light is passed through the tube ▪ Rotation of the polarization plane occurs ▪ Light goes through a second polarizer called the analyzer ▪ The new plane of polarization and degree of rotation can be found by rotating the analyzer until the light passes through it ▪ Angle of rotation is denoted a and is expressed in degrees Optical Activity
Optical Activity Rotation The amount of rotation observed in a polarimetry experiment depends on the number of optically active molecules Number of optically active molecules depends on sample concentration and sample pathlength the pathlength is the length of the sample tube Assigning direction of rotation Levorotatory molecules Optically active molecules that rotate polarized light to the left (counterclockwise) Given the symbol (-as in (-)-morphine Dextrorotatory molecules Optically active a molecules that rotate polarized light to the right (clockwise) Given the symbol (+)as in (+)-sucrose
Rotation ▪ The amount of rotation observed in a polarimetry experiment depends on the number of optically active molecules ▪ Number of optically active molecules depends on sample concentration and sample pathlength ▪ the pathlength is the length of the sample tube Assigning direction of rotation ▪ Levorotatory molecules ▪ Optically active molecules that rotate polarized light to the left (counterclockwise) ▪ Given the symbol (-) as in (-)-morphine ▪ Dextrorotatory molecules ▪ Optically active a molecules that rotate polarized light to the right (clockwise) ▪ Given the symbol (+) as in (+)-sucrose Optical Activity