ORGANIC CHEMISTRY 354

ALKENE INTRODUCTION

NOMENCLATURE

STEREOCHEMISTRY

ALKENES

C=C DOUBLE BOND, A "PI" BOND

CALLED OLEFINS & UNSATURATED

IMPORTANT INDUSTRIALLY

ETHYLENE, 48 BILLION POUNDS/YEAR

PROPYLENE, 28 BILLION POUNDS/YEAR

OCCUR NATURALLY

A PRECURSOR TO VITAMIN A, beta-CAROTENE

GENERAL FORMULA: C_nH_2n

PROVIDES A USEFUL TOOL WHEN STARTING TO DETERMINE STRUCTURE

NOMENCLATURE

1. ENDING IS "ENE"

CH₃CH=CH₂ is PROPENE

2. SELECT CHAIN SO "LONGEST" CHAIN CONTAINS THE DOUBLE BOND.

3. NUMBER CARBONS IN LONGEST CHAIN SO DOUBLE BOND COMES AFTER SMALLEST # CARBON .

4. IF DOUBLE BOND IS EXACTLY IN THE MIDDLE, NUMBER SO FIRST BRANCH POINT HAS SMALLER NUMBER.

5. IF MORE THAN ONE DOUBLE BOND, USE DIENE, TRIENE, TETRAENE, ETC.

6. USE ALKANE RULES:

---LIST GROUPS ALPHABETICALLY

---MUST HAVE A NUMBER FOR EVERY GROUP

---COMMAS BETWEEN NUMBERS

---HYPHENS BETWEEN NUMBERS AND LETTERS examples.

7. CYCLIC COMPOUNDS

---DOUBLE BOND COMES AFTER CARBON 1.

8. COMMON NAMES

--- CH₂=CH₂ ETHYLENE

--- CH₃CH=CH₂ PROPYLENE

--- (CH₃)₂C=CH₂ ISOBUTYLENE

GROUPS

--- CH₂=CH- VINYL GROUP

--- CH₂=CHCH₂- ALLYL GROUP

ALKENE STEREOCHEMISTRY

cis-2-BUTENE

trans-2-BUTENE

NOTE: THE cis-2-BUTENE ISOMER HAS STERIC STRAIN.
trans-2-BUTENE IS MORE STABLE.

cis-, trans-NOMENCLATURE

However--

NEED AN UNAMBIGUOUS METHOD!

THE E,Z DESIGNATION USES PRIORITIZED GROUPS.

NEED SEQUENCE RULES TO ESTABLISH PRIORITIES OF TWO GROUPS ON AN SP² CARBON

1. A. LOOK AT FIRST ATOM IN GROUP. THE HIGHER ATOMIC NUMBER GETS THE HIGHER PRIORITY.

I > Br > Cl > S > F > O > N > C > H

WHICH IS HIGHER IN PRIORITY, N or P?

2-AMINO-1-CHLOROPROPENE

1. b. IF THE ATOMIC NUMBERS ARE THE SAME, THE HIGHER MASS NUMBER (ISOTOPES) GETS THE HIGHER PRIORITY.

WHICH IS HIGHER IN PRIORITY ¹⁶O or ¹⁸O?

1-DEUTEROPROPENE

2. IF YOU CAN'T DECIDE USING THE FIRST ATOM, LOOK TO WHAT IS ATTACHED AND USE PREVIOUS RULES. IF STILL THE SAME, REPEAT UNTIL YOU FIND THE FIRST DIFFERENCE

CH₃CH₂- > CH₃-

-OCH₃ > -OH

-CH₂CH₂CH₂CH(CH₃)₂ > -CH₂CH₂CH₂CH₂CH₂CH₃

WHICH IS HIGHER IN PRIORITY -CH₂CH₂CH(OH)CH₃ or -CH₂CH(OH)CH₂CH₃?

3-CHLORO-2,4-DIMETHYL-3-HEPTENE

3. IF MULTIPLE BONDS ARE IN THE GROUP, TREAT EACH PI BOND AS A SIGMA BOND

cis-, AND trans-RHODOPSIN

cis-, AND trans-RETINAL

cis-, AND trans-RHODOPSIN, INTERACTIVE VIEW