Alkenes

Question 1

Alkenes

• what type of BOND is present? + between what type of atoms?
• aka ____
• general formula

Answer 1

• double bond between 2 carbon atoms
• olefins
• Cn H2n

Question 2

____* and _____* are massively produced worldwide for use in the _____ of many important ______

*CLUE: 2 types of alkenes

Answer 2

• ethylene and propylene
• synthesis
• chemicals

Question 3

PALATANDAAN in naming ALKENES
in terms of:

• suffix
• parent chain (straight-chain) [2]
• parent chain (cyclo) [2]

Answer 3

• -ene
• longest chain that passes thru BOTH C ATOMS in the double bond (with the double bond carbons having the lowest number)
• indicate position of double bond before the parent name
• the 2 double bond carbons are automatically given positions 1& 2
• numbering continues to direction that will give the lowest possible numbers to substituents

Question 4

3 types of ISOMERISM in ALKENES

• same…
• different…

Answer 4

1. Positional Isomerism
   - same molecular formula
   - same carbon skeleton
   - different position of C=C
2. Skeletal Isomerism
   - same molecular formula
   - same position of C=C
   - different skeletal structure/branching
3. Geometric Isomerism
   - same molecular formula
   - same position of C=C
   - different orientation of substituents (cis and trans)

Question 5

2 types of GEOMETRIC ISOMERISM in ALKENES

Answer 5

1. Cis-Trans Isomerism
2. E,Z System

Question 6

Is Geometric Isomerism exhibited by monosubstituted alkenes?

Answer 6

No,

1. Cis-Trans Isomerism - disubstituted alkenes
2. E,Z System - tri- and tetrasubstituted alkenes

Question 7

____-_____ isomers are 2 ____ ____ compounds

+ meaning and reason

Answer 7

• cis-trans
• different isolable

isolated thru different ways due to difference in physical properties

Question 8

WHICH of the 2 is MORE STABLE?

cis or trans isomerism

+ presence of dipole moment
+ strain present

Answer 8

trans - NO steric strain + dipole moment cancels

cis - w/ steric strain + more polar due to dipole moment

Question 9

PALATANDAAN in cis-trans isomerism molecules

Answer 9

IN DI-SUBSTITUTED ALKENES:

if 2 identical substituent groups are attached to 1 carbon in the double bond, it CANT exist as cis-trans isomerism

this is because if you try to determine their cis or trans counterpart, it would result in the exact SAME (identical) molecule

Question 10

In E,Z system

how to determine the configuration? (2 steps)

+ what rule is it based on?

Answer 10

1. assign higher priorities to substituent groups PER carbon atom in the double bond
2. determine configuration thru:
   E - entgegen “opposite”
   Z - zussamen “together

based on cahn-ingold-prelog rules

Question 11

How are compounds written based on the E,Z system?

use the molecules: 1-bromo-1-chloropropene

Answer 11

similar to naming in cis-trans isomerism

(E*)-1-bromo-1-chloropropene

(Z*)-1-bromo-1-chloropropene

*italicized

Question 12

ALKENES have slightly ____ ____ moments compared to ____ due to?… which makes alkenes easily ____

Answer 12

• higher dipole
• alkanes
• loosely held pi electrons
• polarizable

Question 13

the physical properties of alkenes are ____ to those of alkanes

Answer 13

similar

Question 14

ALKENES - Physical States

3 intervals + at what temp?

Answer 14

ROOM TEMP

C2 - C4 and 1-pentene: gases

C5 - C14: liquids

C15: solids

Question 15

ALKENES - DENSITY (1) and SOLUBILITY (3)

Answer 15

• less dense than water
• soluble in non-polar solvents
• soluble in cold concentrated H2SO4 due to chemical reaction
• insoluble in polar solvents (like water)

Question 16

ALKENES - Boiling Point

• main trends
• cis vs trans

Answer 16

SIMILAR TREND TO ALKANES

• straight-chained: longer = higher BP*
• branch-chained: more spherical/branching = lower bp**
• ring: bigger size = higher bp

*due to heavier molecular weight = stronger LDF
**due to less surface area = weaker IMFA

cis-isomers have HIGHER BP than trans-isomers

Question 17

ALKENES - Boiling Point

the more substituents, the ____ the boiling point

Answer 17

HIGHER

considering substituents are attached to the double bond carbon atoms

if the substituents/branching are NOT attached to any of the carbons in the double bond, then it will have LOWER BP

Question 18

ALKENES - Melting Point

• cis vs trans isomers

Answer 18

cis-isomers have LOWER MP than trans isomers

Question 19

2 ways of PREPARING ALKENES

+ what happens
+ draw a sample reaction

Answer 19

1. Dehydrohalogenation of Alkyl Halide
   - alkyl halide reacts with a strong base to eliminate an HX molecule and form an ALKENE
2. Dehydration of alcohol
   - alcohol reactions with a strong acid to eliminate an H2O molecule and form an ALKENE

Question 20

What molecules are considered as alcohols?

Answer 20

molecules with a hydroxyl (-OH) group

Question 21

ALKENES are ___ reactive than ____ due to?

Answer 21

• more
• alkanes
• loosely held pi e- in the pi bond

Question 22

ALKENES have _______ _____ group due to ? that can be donated to ?

Answer 22

• nucleophilic
• C=C
• loosely held pi e- that can be donated to an electrophile (polar reaction)

Question 23

SYN addition vs ANTI addition

Answer 23

SYN: reagent added is on the same face

ANTI: reagent added on opposite faces

Question 24

RANK the NUMBER of alkyl substitutions in terms of stability and △H value

Answer 24

LEAST STABLE (HIGHEST △H VALUE)

UNsubstituted
MONOsubstituted
DIsubstituted
TRIsubstituted
TETRAsubstituted

MOST STABLE (LOWEST △H VALUE)

Question 25

ALKENE STABILITY 2 FACTORS

Answer 25

1. Hyperconjugation 2. Bond Strength

Question 26

ALKENE STABILITY - HYPERCONJUGATION - ______ interaction between the _______ ____ bond and ______ ______ bonds on substituents in simpler terms?

Answer 26

- stabilizing - C=C pi - C-H sigma if no alkyl substituent groups (less C-H bonds are present, like ethene), the molecule is less stable. the more alkyl substituent groups (and the more C-H bonds), the more stable the molecule

Question 27

ALKENE STABILITY - BOND STRENGTH - ___ -____ (hybridization) bond is stronger than ____-____ (hybridization) bond - wherein, the _____ _____ substituted alkenes will have a higher ratio of ____-____ bonds, and thus, ____ stable + in simpler terms?

Answer 27

- Csp2 - Csp3 - Csp3 - Csp3 - more highly - Csp2 - Csp3 - more INTERNAL ALKENES are more stable and have stronger bonds than terminal alkenes

Question 28

HI vs HBr vs HCl rank in terms of: - acid strength - bond strength - most reactive - fastest reaction

Answer 28

strongest acid - most reactive - fastest reaction - weakest bond strength HI HBr HCl weakest acid - least reactive - slowest reaction - strongest bond strength

Question 29

MARKOVNIKOV'S RULE - main principle + its 2 concepts? - ^^ is based on?? + its 2 concepts? CONSEQUENCE/FINAL RESULT?

Answer 29

LAW OF ELECTROSTATICS 1. dispersal of charge (more alkyl groups = more stable): 4° carbon/carbocation 2. charge intensified (less alkyl groups = more concentrated at one place = less stable): 1° carbon/carbocation based on CARBOCATION STABILITY 1. Inductive effect 2. Hyperconjugation - hydrogen atoms attach to less substituted (more hydrogen atoms attached) carbon atom - other groups attach to more substituted carbon atom

Question 30

3 types of CARBOCATION STABILITY + process + number of products

Answer 30

1. No rearrangements (1 product) 2. w/ rearrangements via 1,2 - Hydride Shift (2 products) - after initial carbocation, rearranges to form another significant product - H atom of adjacent 3° carbon SWITCHES PLACE with X atom in double bond 2° carbon 3. w/ rearrangements via 1,2 - Methyl/Alkyl Shift (2 products) - after initial carbocation, rearranges to form another significant product - methyl/alkyl group of adjacent 4° carbon SWITCHES PLACE with X atom in double bond 2° carbon