Review Flashcards by Juliette Repole

Chemical bonding is dictated by […]

Valence electrons

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What are valence electrons?

Electrons in the outermost shell (equal to the group #)

Rule of thumb: atoms form bonds in a manner that fills outer shell (e.g., octet rule)

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Which ions tend to form ionic bonds?

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How is formal charge calculated?

Charge = (# valence e-) - (# bonds) - (# unshared e-)

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Briefly - what is VSEPR theory?

Bonded atoms/electron pairs try to maximize space/repulsions and determine the shape of the molecule.

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What are the 4 numbers that describe atomic orbitals?

Energy level or shell (n) : 1, 2, 3, …

Angular momentum; defines shape (s - sphere; p = lobes) (l): ** 0 (‘s’ orbital); 1 (‘p’ orbital); 2 (‘d’ orbital), …
Magnetic quantum number (m): values from -l to +l (thus, an s orbital has m = 0, while a p orbital has m = -1, 0, +1) Spin number (s)** : each electron has spin

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Describe atomic orbitals energy level diagrams.

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Describe atomic orbital hybridization to form molecular orbitals.

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Rotation of atoms around a sigma bond affects bond energy.
True or False?

False.

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Rotation of atoms around a sigma bond does not affect the bond energy.
True or False?

True.

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sp3 hybridization

Single bonding

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sp2 hybridization

Double bonding

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Pi bonds result from:

Overlap of 2p atomic orbitals

Rotation about a pi bond is disfavoured - imposes planar geometry

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Pi bonds are weaker than sigma bonds.
True or False?

True.

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Sigma bonds are weaker than pi bonds.
True or False?

False.

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sp hybridization

Triple bonding

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What is resonance and when is it possible?

Delocalized molecular orbitals; only possible with overlapping, parallel p orbitals

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Describe the bond dissociation energies and lengths.

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Alkane

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Alkene

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Conjugated alkene

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Alkyne

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Arene

e.g., benzene

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Ketone

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Aldehyde

Carboxylic acid

Ester

Acid Halide

Amide

Peroxy Acid

Anhydride

Primary Amine

Secondary Amine

Tertiary Amine

Alcohol

Ether

Thiol

Thioether

Alkane

Alkene

Conjugated alkene

Alkyne

Arene ## Footnote e.g., benzene

Ketone

Aldehyde

Carboxylic acid

Ester

Acid Halide

Amide

Peroxy Acid

Anhydride

Primary Amine

Secondary Amine

Tertiary Amine

Alcohol

Ether

Thiol

Thioether

Define: polarity

Uneven sharing of electron results in a dipole

Describe the order of increasing electronegativity. ## Footnote More capable of carrying negative charge

S = C < N < O < F

List non-covalent interactions from strongest to weakest.

* **Ion-ion** (very strong) * Lattice interactions (188 kcal/mol) stronger than typical covalent bonds (100 kcal/mol) * **Ion-dipole** (moderately strong) * Greater the charge = stronger * **Dipole-dipole** (weak) * Polar interactions * **Dipole-induced dipole** (quite weak) * **Instantaneous dipole-induced dipole** (very weak) * Non-polar interactions (a.k.a. London forces)

Describe hydrogen bonding.

* A special kind of dipole-dipole * *H-bond donor* must be an electronegative atom (N, O, F) * *H-bond acceptor* must be an electronegative atom * H-bond strength of ~2-8 kcal/mol (distance/orientation dependent)

Describe the strength of hydrogen bonds in water.

O-O distance is dependent on H-bond strength of water

Describe the molecular geometry of water.

* Bent tetrahedral geometry is crucial to water's special properties and ability to form hydrogen bond networks

Describe hydrogen bonding in ice.

Describe hydrogen bonding with food components. [5]

Briefly describe water interaction with proteins.

Bound water can be crucial to enzyme activity and stability of folded structure.

Describe the hydrophobic effect.

Driven by increased entropy (lower energy) due to the release of solvation water from non-polar groups.

What is the general formula for CHO?

What are sugars?

* Polyalcohols with an aldehyde or ketone group; named according to the type of carbonyl functional group

What is an enantiomer?

Non-superimposable mirror images

What is the difference between D and L forms of sugar?

D = hydroxyl of highest # chiral C is on right side of Fischer projection (by convention)

L-sugars are rare - only two are commonly found in food (as polysaccharides). They are:

* L-arabinose * L-galactose

What are the D-aldose sugars?

What are the D-ketose sugars?

How do sugars form rings?

Base catalyzed

What are the bonds in each disaccharide?

**Lactose**: Beta-(1-4) linkage between galactose-glucose **Sucrose**: alpha-(1-2) linkage between glucose-fructose **Maltose**: alpha-(1-4) linkage between glucose-glucose

When is a sugar non-reducing?

When a glycosidic linkage forms between two anomeric carbons ## Footnote A reducing sugar is one that reduces another compound and is itself oxidized; that is, the carbonyl carbon of the sugar is oxidized to a carboxyl group. A sugar is classified as a reducing sugar only if it has an open-chain form with an aldehyde group or a free hemiacetal group.

Describe polysaccharides.

What is amylose?

Mostly linear polysaccharide with a reducing end and a non-reducing end

Describe the structure of amylose.

Left-handed double helix at 6 glucose molecules per turn

What is amylopectin?

Branded polysaccharide

Describe the structure of amylopectin.

* Similar to glycogen, which is > highly branched; smaller * Branches also form helical structure, similar to amylose * Waxy starches consist mainly/only of amylopectin

What are starch granules?

Starch gelatinization is irreversible. True or False?

True.

Starch gelatinization is reversible. True or False?

False.

Starch granules are insoluble in 'cold' water'. True or False?

True.

Starch granules are soluble in 'cold' water. True or False?

False.

Describe starch gelatinization.

* Heating in water induces gelatinization: * Water penetrates into amorphous regions * Disruption of molecular order * Loss of crystallinity * Leaching of amylose * Granules swell many times their normal size * Easily disrupted by stirring * Produce a viscous mass (starch paste)

What is the difference between saturated and unsaturated fatty acids?

Why does unsaturation add 'kinks'?

Name 3 important PUFAs.

What are acylglycerols?

Describe how the melting point of a fatty acid is affected by chain length and saturation.

* MP increases with chain length (because the intermolecular forces, such as van der Waals forces, are stronger with longer chains) * MP decreases with unsaturation (double bonds create kinks in the chain, preventing the molecules from packing closely together; weaker molecular packing reduces the strength of intermolecular forces)

What is the difference bewteen simple and mixed triacylglycerols?

What is a phospholipid?

* An acylglycerol with one hydroxyl group (sn-3) esterified to a phosphate group

What is the primary component of cellular membranes?