Alkanes, Cycloalkanes And Alkyl Halides (w19) Flashcards
What happens to non polar molecules ?
Non-polar molecules: dissolve in non-polar or weakly polar organic solvents and are hydrophobic
Non-polar molecules are ____ dense than water and ____ in water.
Less
Insoluble
When does bond rotation occur in conformational isomers ?
Occurs in single bonds but not double bonds
Each structure is generated by the rotation is a what ?
A conformer or conformational isomer
What is GAUCHE ?
Gauche:
When all the bonds are staggered, but the big substituents, so the two methyl groups are still near one another
What is the conformational equilibrium of an alkane ?
When the energy relative to anti conformation is plotted against the dihedral angle
What are the two distinct faces of a cycloalkane ?
- two substituents point towards the same face (CIS)
- two substituents point towards the opposite face (TRANS)
What can’t the geometric isomers of cycloalkanes do ?
They can’t interconvert without breaking and re-forming bonds
What is the general formula of cycloalkanes ?
CnH2n
General formula of alkanes ?
CnH2n+2
What may cycloalkanes experience during conformation ?
Angle strain and torsional strain (ring strain), this can be reduced by deviating from a planar structure
What does the preferred bond angle of 109.5 of a C sp3 tetrahedral carbon do to the electrons ?
Places the electron clouds as far away from one another as possible
What would cyclohexane suffer from if it was flat ?
Suffer from angle and torsional strain.
Can cyclohexane flip between chair conformations ?
Yes
What is chair conformation ?
Chair
Lowest energy – all H are as far apart as possible – so is the most stable
What is boat conformation ?
Boat
Unfavourable steric interactions – some H too close - and is less stable.
What do substituents on cyclohexane prefer to be ?
Prefer to be equatorial rather than axial
What do larger substituents give ?
They give a greater preference for the equatorial position
What does preference of disubstituted cyclohexane depend on?
Depends on the substituents and their relative stereochemistry
What occurs at equilibrium of disubstituted cyclohexane ?
The upper conformer dominates (98%) and both groups are equatorial
What is the carbon-halogen bond ?
Polar - so is easy to break
What are nucleophiles ?
- Nucleophiles “love nuclei” and wish to form bonds by donating or sharing their electrons
- Nucleophiles are electrons rich and can be negative ions, or neutral molecules with electron lone pairs
What are electrophiles ?
- Electrophiles “love electrons” and wish to form bonds by accepting electrons or sharing electrons with a reactant molecule.
- Electrophiles are electron deficient and can be positive ions or neutral (but δ+) molecules
Does a nucleophile have a lone pair of electrons or does this apply to an electrophile?
Nucleophiles have a lone pair of e-
- they are electron donors and electrophiles are e- acceptors
What is nucleophilic substitution ?
Nucleophilic substitution: nucleophile (Nuc∶-) replaces a leaving group (X−) from a carbon atom, using its lone pair of electrons to form a new bond to the carbon atom
What is an elimination reaction ?
Elimination reaction: halide ion leaves along with another atom or ion (often H+), a new pi bond results. Dehydrohalogenations (H-X). Reagent (B:-) reacts as a base. Most nucleophiles are also basic and can engage in either substitution or elimination, depending on the alkyl halide and the reaction conditions
What are curly arrows ?
A way to understand reaction mechanisms and can be applied to the understating if mechanisms of biological processes and the action of drugs
What is a double headed arrow used to show ?
A double-headed arrow is used to show the movement of a PAIR of electrons
(from where they are to where they are moving)
What is a single-headed arrow used to show ?
Occasionally you may encounter single-headed arrow. This is used to show the movement of a SINGLE electron
What does a single covalent bond contain ?
Two electrons
Which direction does a curly arrow go ?
From nucleophile to an electrophile
