Optical Isomerism
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What are the three ways structural isomers differ? • FGI - diff. fnctl. grps. • PI - fcntl. grps. atchd. diff. pnts. - mn. crbn. chn. 3.CI - hve. diff. arngmnts. - C skltn. mlcle.
They differ through having: Functional group isomerism - different functional groups Positional isomerism - functional groups attached to different points to the main carbon chain Chain isomerism -having different arrangements of the carbon atoms in the skeleton of the molecule
What is stereoisomerism, and what are the two types? (cmpnds. hve. strcl. frmla. - diff. arngmnt. atms. spce.) EZ + optcl.
When compounds have the same structural formula but differ in the arrangement of atoms in space The two types are E-Z isomerism and optical isomerism
What is optical isomerism? (frm. sterossm. - sngle. chrl. cntre. ctrs. non. sprimpsbl. mirr. imgs. knwn. entmrs.)
A form of stereoisomerism where a single chiral centre creates non - superimposable mirror images known as enantiomers
When do optical isomers occur? (ocrs. whn. crbn. atm. atchd. 4 diff. sbstnts.)
Optical isomers occur when a carbon atom is attached to four different substituents
What are pairs of non - superimposable mirror image molecules called?
Enantiomers
Why are certain molecules called optical isomers? (dffr. wy. rte. plne. plrsd. lght.)
They differ in the way they rotate the plane of polarised light
How do optical isomers rotate plane - polarised light? (rte. clckwse. + othr. antclckwse.)
One rotates it clockwise ((+)-isomer) and the other anticlockwise ((-)-isomer)
What are the two optical isomers of a chiral molecule called?
They are called a pair of enantiomers
What are enantiomers? (mlcls. - non sprimpsble. mror. imgs. echothr.)
Molecules that are non-superimposable mirror images of each others
What is the carbon atom bonded to four different groups called?
It is called the chiral centre
How can you recognise a chiral molecule? (cntns. lst. 1 cntrl. atm. bndd. - fr. diff. grps.)
A chiral molecule contains at least one central atom bonded to four different groups
How can light be polarised? (psng. thru. plrd. fltr. - wch. oly. alws. vbrtns. 1P pss thru.)
By passing it through a polaroid filter, which only allows vibrations in one place to pass through
What does light consist of? (cnsts. vbrtng. elctrc. + mgntc. fld. - lke. wvs. vbrtng. all. drctns. - rght. agls. - drctn. mtn.)
Light consists of vibrating electric and magnetic fields, like waves vibrating in all directions at right angles to the direction of motion
What is polarised light? (plrd. lght. vbrts. - 1P aftr. psng. thru. plrd. fltr.)
Polarised light vibrates in just one plane after passing through a polaroid filter
What instrument is used to measure optical rotation? (plrimtr.)
A polarimeter is used to measure the rotation of plane - polarised light
What does the (+)-isomer do to plane - polarised light?
The (+)-isomer rotates the plane of polarisation clockwise by a specific angle
What does the (-)-isomer do to plane polarised light?
The (-)-isomer rotates the plane of polarisation anticlockwise by the same angle
Draw the 3D diagrams to show both stereoisomers for: 2-chlorobutane
Check your answer on notes +
Compare EZ isomers to optical isomers • chiral centres? • superimposability?
Optical isomers contain chiral centres, whereas EZ isomers have none. EZ isomers are superimposable, whereas optical isomers are not.