Lecture 12-Organic Chemistry II Flashcards
Name the 5 types of chains + rings and whether they’re acyclic + cyclic?
Aliphatic (Acyclic)
Saturated + unsaturated (Acyclic)
Alicyclic (Cyclic)
Aromatic (Cyclic)
Heterocyclic (Cyclic)
Alicyclic?
Compounds containing a ring of saturated carbon atoms
Aromatic?
Contain a ring where all the atoms are unsaturated + conjugated
Heterocyclic?
Contain a ring made up of carbon + at least 1 other element = N,S,O
A functional group in a molecule …..
gives characteristic chemical properties
acts as a site of chemical reactivity
serves as the basis for nomenclature
classifies its family
What’s a polyfunctional compounds?
Contain more than 1 functional group
What determines the class in a polyfunctional compounds?
Primary functional group
Secondary functional group = substituents
What is the order of preference for principal group is
Carboxylic acid - ester - acid halide - amide - nitrile - aldehyde - ketone - alcohol - amine - double bond - triple bond - halogen - nitro
What is the homologous series?
A group of similar compounds with similar chemical properties in which members contain the same functional group ,but differ by the length of the C chain : adjacent members differ by a CH2 unit
What are successive members of a homologous series called?
Homologues
Describe the properties of homologous series?
- same general formula
- prepared similar methods
- similar chemical properties
- gradual variation in physical properties with increasing molecular weight
What is a hybrid atomic orbital?
Combination of atomic orbitals from the same atom
What is a molecular atomic orbital?
Combination of atomic / hybrid atomic orbitals from different atoms
How so second row elements (C,O,N) hybridize using what orbitals?
2s , 2p —-> sp,sp2,sp3 HAOs
Describe a s orbital?
spherical
lower in energy than other orbitals in the same shell
Describe a p orbital?
dumb-bell shape
nodal plane passes through nucleus
higher in energy than s-orbital
3 p orbitals in the same shell
Explain hybridisation using carbon as an example?
C electronic configuration = 1s2 2s2 2p2
- 2 unpaired e- ,but cC can form 4 bonds THEREFORE …
- 1 of the 2s e- can be promoted —> vacant p orbital
,But this requires energy input
it’s favourable ,because of decreased electron-electron repulsion
-the 2s + 2p orbitals now mix —> various hybrid atomic orbitals
Sp3
- All 4 atomic orbitals combine —> same n.o. of new hybrid atomic orbitals
- All 4 sp3 orbitals = equivalent with the same energy (degenerate)
- Orbitals point towards the corners of a tetrahedron
- Overlap produces sigma bonds
- Used for bonding in saturated compounds
Sp2
- The s + p orbitals combine —> 3 new hybrid atomic orbitals
- The 3rd p orbital = unchanged
Sp2 orbitals point towards the corners of a triangle
-used for sigma bonding
The p orbital is perpendicular to them
-used for pi bonding
Sp2 hybridisation used for bonding in alkenes,carbonyls + aromatic rings
Sp?
- The s + 1p orbital combine —> 2 new hybrid atomic orbitals
- The other 2 =unchanged
Sp orbitals = 180.C to one another (linear)
-used for sigma bonding
Sp hybridisation = used for bonding in alkynes + nitriles
What are the properties of hybrid orbitals?
Hold e- closer to nucleus
The bond —> shorter + stronger
More directional = more effective bonding interactions
More s-character in an orbital —> lower the energy
-increased stability of an e- in that orbital
The overlapping of orbitals forms 2 types of bonds depending on?
The geometry of overlap
How are sigma bonds formed and describe their properties?
Formed by direct overlap
- e- density is along the line of the bond
- symmetric wrt rotation about the bond
- bond may be formed between s-s , p-p , s-p or hybridized orbitals
The bonding molecular orbital is lower in energy than the original atomic orbitals
How are pi bonds formed?
By parallel overlap of p orbitals
- electron affinity is above+below the plane of the bond
- form after sigma bonds
- higher in energy than sigma bonds —> weaker + more easily broken
Name molecules with sigma bonding?
Methane
Ethane
What type of bonding is there in a double bond? (2 pairs of shared e-)
1 sigma bond
1 pi bond
What type of bonding is there in a triple bond? (3 pairs of shared e-)
1 sigma bond
2 pi bonds
What is the bonding framework in ethyne (acetylene)?
Sigma bonds
pi overlap in ethyne
Describe the bonding in benzene?
pi e- delocalised around the ring, above + below the plane
-all bond lengths identical (between single +double bonds)
WHat type of bond has the longest length and which one has the most strength?
Longest = single --> double --> triple Strongest = triple --> double --> single
