Alkenes Flashcards
Alkenes
- what type of BOND is present? + between what type of atoms?
- aka ____
- general formula
- double bond between 2 carbon atoms
- olefins
- Cn H2n
____* and _____* are massively produced worldwide for use in the _____ of many important ______
*CLUE: 2 types of alkenes
- ethylene and propylene
- synthesis
- chemicals
PALATANDAAN in naming ALKENES
in terms of:
- suffix
- parent chain (straight-chain) [2]
- parent chain (cyclo) [2]
- -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
3 types of ISOMERISM in ALKENES
- same…
- different…
- Positional Isomerism
- same molecular formula
- same carbon skeleton
- different position of C=C - Skeletal Isomerism
- same molecular formula
- same position of C=C
- different skeletal structure/branching - Geometric Isomerism
- same molecular formula
- same position of C=C
- different orientation of substituents (cis and trans)
2 types of GEOMETRIC ISOMERISM in ALKENES
- Cis-Trans Isomerism
- E,Z System
Is Geometric Isomerism exhibited by monosubstituted alkenes?
No,
- Cis-Trans Isomerism - disubstituted alkenes
- E,Z System - tri- and tetrasubstituted alkenes
____-_____ isomers are 2 ____ ____ compounds
+ meaning and reason
- cis-trans
- different isolable
isolated thru different ways due to difference in physical properties
WHICH of the 2 is MORE STABLE?
cis or trans isomerism
+ presence of dipole moment
+ strain present
trans - NO steric strain + dipole moment cancels
cis - w/ steric strain + more polar due to dipole moment
PALATANDAAN in cis-trans isomerism molecules
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
In E,Z system
how to determine the configuration? (2 steps)
+ what rule is it based on?
- assign higher priorities to substituent groups PER carbon atom in the double bond
- determine configuration thru:
E - entgegen “opposite”
Z - zussamen “together
based on cahn-ingold-prelog rules
How are compounds written based on the E,Z system?
use the molecules: 1-bromo-1-chloropropene
similar to naming in cis-trans isomerism
(E*)-1-bromo-1-chloropropene
(Z*)-1-bromo-1-chloropropene
*italicized
ALKENES have slightly ____ ____ moments compared to ____ due to?… which makes alkenes easily ____
- higher dipole
- alkanes
- loosely held pi electrons
- polarizable
the physical properties of alkenes are ____ to those of alkanes
similar
ALKENES - Physical States
3 intervals + at what temp?
ROOM TEMP
C2 - C4 and 1-pentene: gases
C5 - C14: liquids
C15: solids
ALKENES - DENSITY (1) and SOLUBILITY (3)
- less dense than water
- soluble in non-polar solvents
- soluble in cold concentrated H2SO4 due to chemical reaction
- insoluble in polar solvents (like water)
ALKENES - Boiling Point
- main trends
- cis vs trans
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
ALKENES - Boiling Point
the more substituents, the ____ the boiling point
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
ALKENES - Melting Point
- cis vs trans isomers
cis-isomers have LOWER MP than trans isomers
2 ways of PREPARING ALKENES
+ what happens
+ draw a sample reaction
- Dehydrohalogenation of Alkyl Halide
- alkyl halide reacts with a strong base to eliminate an HX molecule and form an ALKENE - Dehydration of alcohol
- alcohol reactions with a strong acid to eliminate an H2O molecule and form an ALKENE
What molecules are considered as alcohols?
molecules with a hydroxyl (-OH) group
ALKENES are ___ reactive than ____ due to?
- more
- alkanes
- loosely held pi e- in the pi bond
ALKENES have _______ _____ group due to ? that can be donated to ?
- nucleophilic
- C=C
- loosely held pi e- that can be donated to an electrophile (polar reaction)
SYN addition vs ANTI addition
SYN: reagent added is on the same face
ANTI: reagent added on opposite faces
RANK the NUMBER of alkyl substitutions in terms of stability and △H value
LEAST STABLE (HIGHEST △H VALUE)
UNsubstituted
MONOsubstituted
DIsubstituted
TRIsubstituted
TETRAsubstituted
MOST STABLE (LOWEST △H VALUE)
ALKENE STABILITY
2 FACTORS
- Hyperconjugation
- Bond Strength
ALKENE STABILITY - HYPERCONJUGATION
- ______ interaction between the _______ ____ bond and ______ ______ bonds on substituents
in simpler terms?
- 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
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?
- Csp2 - Csp3
- Csp3 - Csp3
- more highly
- Csp2 - Csp3
- more
INTERNAL ALKENES are more stable and have stronger bonds than terminal alkenes
HI vs HBr vs HCl
rank in terms of:
- acid strength
- bond strength
- most reactive
- fastest reaction
strongest acid - most reactive - fastest reaction - weakest bond strength
HI
HBr
HCl
weakest acid - least reactive - slowest reaction - strongest bond strength
MARKOVNIKOV’S RULE
- main principle + its 2 concepts?
- ^^ is based on?? + its 2 concepts?
CONSEQUENCE/FINAL RESULT?
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
3 types of CARBOCATION STABILITY
+ process
+ number of products
- No rearrangements (1 product)
- 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 - 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
