Chapter 13 - Alkenes Flashcards
alkenes contain at least?
one C=C
GF?
CnH2n
Have similar ?
Chemical and physical properties
the π bond can only form after?
σ bond is formed
π bond?
- is a region of high electron density - the bond is the reactive region of the molecule
- restricts the rotation around the C=C
in the region of the double bond, they have a ? shape
flat, are ‘planar’
shape around C=C?
Trigonal Planar - 120 bond angle
are ? reactive than alkanes?
more
uses of hydrogenation?
- Veg and animal oil/ fats have a high proportion f unsat fats
- presence of C=C means chains don’t fit well together
➡ liquids at room temp ➡ makes them difficult to use as spread? - but we can change this
how can we change it (uses of halogenation cont.)?
- by hydrogenating the fats, we can raise their b.p.
- bc sat. fats have higher bp ➡ this produces margarine
but there are some ____ of incl unsat. fats in the diet?
benefits
are there are also some ____ of eating certain sat. fats?
Negatives
transfats?
- the high temps in this process produce a trans arrangement of molecules
- called trans-fats- these are thought to contribute to raised cholesterol levels
- this can have many negative impacts on health
when can 2 products be formed ?
when a H halide is added to an unsymmetrical alkene
what are polymers?
macromolecules, made from small repeating units - monomers
which bond is broken in the monomer in polymerisation?
- the π bond
- the electrons from these bonds are used to make sigma bonds w neighbouring C atoms
steps to deduce the structure of the polymer from monomer?
1: draw monomer w the C=C as the focus
2: draw square brackets around the monomer
3: change monomer to polymer- change C=C ➡C-C and draw 2 lines extending from each C THROUGH []
4: add subscript n (left side)
steps to deduce monomer from polymer?
1: identify repeating unit
2: draw monomer w C-C as focus
3: Change C-C ➡ C=C
What are addition polymers used in?
plastics, clothing
Problem with addition polymers: crude oil?
are often made from materials derived from crude oil - a non- renewable resource - there’s a finite amount of it
Problem with addition polymers: very stable?
- Addition polymers are very stable bc they are sat. organic compounds
- plastics they make can remain chemically unchanged for a number of years
- as household waste is aroun 10% plastic, this is a problem
how polymers r dealt with?Landfil?
- rubbish and waste can be buried in large holes
- the non biodegradable nature of a lot of this waste can make it a danger for wildlife
how polymers r dealt with? combustion?
- plastics can be burnt
- this process releases: CO2 - greenhouse gas
- depending on how the plastic burns, can als release other chems inlcu: Hydrogen Chloride gas - toxic but can be removed using gas scrubbers
how polymers r dealt with? combustion- useful?
- plastics can be burnt in power stations & the energy released can be sued to generate electricity
how polymers r dealt with? reusing?
- an alt. to landfill
- some plastics can be used more than once
Bioplastics?
- are even more sustainable than biodegradable polymers
- are materials made from renewable resources that are biodegradable
- contain only biodeg. polymers
- if the plant starch is grown sustainably, then the plastic is ‘carbon neutral’
carbon neutral meaning?
the C released is offset by that taken in
issues with bioplastics?
- land is needed to grow th plants ➡ this land could be used in other ways - e.g. to grow food
- the polymer breaks down in the envir so they cannot be used in other, useful ways - e.g. electricity production
problem with photodegradable polymers?
a lack of light such as in the bottom of a landfill pit may mean that these plastics don’t break down
E/Z isomers - Z?
- stands for Zusammen - german for together
- highest priority substituents on the same side of C=C
- Add Z- to normal name
E/Z isomers -E?
- E stands for entgegen - german for opposite
- highest priority substituents on opposite sides of C=C
- E- infront of normal names
Naming E/Z isomers steps?
1: draw the c=c as the focus
2: assign priorities
3: decide if isomer is E or Z
4: add E- or Z- in front of NORMAL NAME
E isomer =
Trans Isomer
Z isomer =
Cis Isomer
what is Zcis?
what does each line of the arrow head show?
the movement of 1 ELECTRON
- a ➡ (arrow with 2 lines) shows movement of a PAIR
what is bond fission?
breaking of chemical bonds
the fission of covalent bonds can be classified into 2 categories:?
homolytic or heterolytic
homolytic fission?
(homo = same, think homosexual)
- when the bond breaks, each electron goes to diff atom in the bond
- results in the formation of free radicals
heterolytic fission?
- when the bond breaks both electrons in the pair go to the same atom in the bond
- results in the formation of ions
bond formation?
- can be regarded as the opp. of bond fission
- bonds r formed on the collision of: 2 free radicals or oppositely charged ions
structural formula include?
the double bond
shape?
trigonal planar, 120 degrees
sigma bonds are formed when?
orbitals overlap between bonding atoms
A double bond is made up of?
a sigma and a pi bond
when does a pi bond form?
when adjacent p orbitals overlap sideways above and below the bonding C atoms
stereoisomerism must have?
diff groups on both C atoms of C=C - not diff one side and same the other