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Quiz 03 Review: Hydrocarbons, Functional Groups, and Lipids

Hydrocarbons and Functional Groups

  • Key ideas about hydrocarbons

    • Hydrocarbons differ by:

    • Length (number of carbon atoms)

    • Branching (degree of branching in the carbon skeleton)

    • Number and position of carbon–carbon double bonds (alkenes) or triple bonds (alkynes)

    • Presence or absence of rings

    • Hydrogen bonding capabilities

    • Pure hydrocarbons (consisting only of C and H) generally cannot participate in hydrogen bonding because they lack highly electronegative atoms (O, N, F) with lone pairs to donate/accept H-bonds.

    • Hydrogen bonding becomes relevant when functional groups containing electronegative atoms are present (e.g., OH, NH, COOH).

    • Functional group shorthand (from transcript):

    • a. Hydroxyl

    • b. Carbonyl

    • c. Carboxyl

    • d. Amino

    • e. Sulfhydryl

    • f. Phosphate

    • g. Methyl

  • Question 3: Which functional group is nonpolar? (single best answer)

    • Answer implied: g. Methyl

    • Rationale: Methyl groups are nonpolar; most other listed groups contain heteroatoms and polar character.

  • Question 4: According to the figure, which functional groups can exist in an ionic state? (Multiple answers; type letters in alphabetical order, no spaces or commas)

    • Likely ionic-capable groups: c. Carboxyl, d. Amino, e. Sulfhydryl, f. Phosphate

    • Rationale and notes:

    • Carboxyl groups can lose a proton to form carboxylate (COO−).

    • Amino groups can gain a proton to form ammonium (NH3+) or, if relevant, be deprotonated to NH2 (neutral; ionization is context-dependent).

    • Sulfhydryl groups (–SH) can lose a proton to form thiolate (S−).

    • Phosphate groups can be ionized (e.g., –O–PO3^2− in physiological contexts).

    • Hydroxyl (a) is typically not ionized under physiological conditions; methyl (g) is not ionizable.

  • Question 5: Which functional group is involved in alcohols?

    • Answer: a. Hydroxyl

    • Note: Alcohols are characterized by the –OH group, which confers polarity and hydrogen-bonding capability.

  • Question 6: Which functional group is an ion in its protonated state?

    • Answer: d. Amino

    • Rationale: In protonated form, amino groups appear as –NH3^+ (positively charged).

  • Question 7: Which functional group is an ion in its deprotonated state?

    • Answer (Multiple): c. Carboxyl, e. Sulfhydryl, f. Phosphate

    • Rationale: deprotonated states can carry a negative charge: carboxylate (–COO−), thiolate (–S−), and phosphate species (various –O–P orientations with negative charges).

  • Question 8–13 involve an image-based molecule

    • 8. What type of functional group is highlighted in the molecule below?

    • Cannot determine from transcript alone without the image.

    • 9. What is a more specific name for the functional group above? [This one is accidentally a short answer, so just input a or b for your answer]

    • Options: a. Ketone b. Aldehhyde

    • Answer depends on whether the highlighted group is a ketone (internal C=O) or an aldehyde (terminal C=O).

    1. Examine the figure below. Which form of the amino group (A or B) is its base form (conjugate base)?

    • Answer cannot be determined without the image.

    1. Which form of the amino group (A or B) is its protonated form?

    • Answer cannot be determined without the image.

    1. If a strong base was added to the solution containing an amino group as in the figure above, which form of the amino group would increase in concentration?

    • Conceptual answer: the deprotonated (base) form would increase; the exact label depends on which form is A or B in the image.

    1. “All functional groups when in their deprotonated states are also in their ionized state.” (hint: compare the protonated states of amino groups and carboxyl groups)

    • Answer: b. False

    • Explanation: Deprotonation of amino groups gives neutral NH2 (not necessarily ionized), whereas carboxyl deprotonation gives COO− (ionized). This shows not all deprotonated states are ionized.

Lipids

  • Question 14: What type of lipid contains two fatty acids and has a polar “head”?

    • Answer: b. Phospholipid

    • Notes: Phospholipids have a glycerol backbone, two fatty acids (nonpolar tails), and a polar head group (often containing phosphate).

  • Question 15: What type of lipid contains several rings?

    • Answer: c. Sterol

    • Notes: Sterols (e.g., cholesterol) have fused ring structures.

  • Question 16: What kind of lipid is testosterone?

    • Answer: c. Sterol

    • Notes: Testosterone is a steroid, a type of sterol.

  • Question 17: Lipid bilayers and micelles are structures that can be formed by _ in aqueous solutions.

    • Answer: b. Phospholipid

    • Notes: Amphipathic phospholipids spontaneously form bilayers or micelles in water due to hydrophobic tails and hydrophilic heads.

  • Question 18: What terms apply to the molecule above? [Multiple answers, short answer] (answer in the form abc. No commas, no spaces, no words.)

    • Options: a. fat, b. Fatty acid, c. saturated, d. Unsaturated, e. Trans

    • Without the image, exact choice cannot be determined; general concepts:

    • If the molecule shown is a triglyceride, you might select a and b depending on context.

    • Saturation: a fatty acid chain can be saturated (no C=C) or unsaturated (one or more C=C).

    • Trans: if the double bond is trans, “Trans” would apply; if cis, it would not.

  • Question 19: What functional group does every fatty acid have?

    • Answer: d. Carboxyl group

    • Notes: Fatty acids terminate in a carboxyl group (–COOH).

  • Question 20: What is the name of the covalent bond that links a fatty acid to a molecule of glycerol?

    • Answer: c. Ester linkage

    • Notes: Fatty acids are esterified to glycerol via ester bonds.

  • Question 21: Are triacylglycerols polymers?

    • Answer: a. no

    • Notes: They are esters of glycerol with three fatty acids, not polymerized chains.

  • Question 22: When comparing two fats with all else being equal, the one made up of fatty acids with longer carbon chains will have a __ melting temperature.

    • Answer: a. Higher

    • Notes: Longer chains increase van der Waals interactions, raising mp.

  • Question 23: When comparing two fats with all else being equal, the one made up of less saturated fatty acids will have a __ melting temperature.

    • Answer: b. lower

    • Notes: Fewer double bonds (more saturation) raise mp; more unsaturation lowers mp due to kinks preventing tight packing.

  • Question 24: Two fatty acids have exactly the same number of carbons and a single carbon–carbon double bond. Fatty acid A has a cis-double bond. Fatty acid B has a trans-double bond. Which fatty acid will have the higher melting point (more likely to be a solid at room temperature)?

    • Answer: b. Fatty acid B

    • Explanation: Trans double bonds allow straighter chains that pack more tightly, raising mp relative to cis isomers.

  • Question 25: Which of the following molecules has a trans double bond?

    • Answer: a. Neither / c. Left / d. Right (image-dependent)

    • Note: Without the provided figure, the correct choice cannot be determined from transcript alone.

  • Question 26: The fact that a discrete part of a phospholipid is polar and another part is nonpolar means that phospholipids are…

    • Answer: b. Amphipathic

    • Notes: Amphipathic molecules have both hydrophilic and hydrophobic regions, enabling membrane assembly.

  • Real-world connections and implications

    • Structure–property relationships: chain length, saturation, and geometry (cis/trans) dictate melting temperatures and membrane behavior.

    • Membrane biology: phospholipid amphipathicity drives bilayer formation, affecting permeability and fluidity.

    • Metabolism and signaling: ionizable functional groups (amino, carboxyl, phosphate) modulate molecular charge, solubility, and interactions in physiological contexts.

    • Ethically/social context: understanding lipids underpins nutrition science, lipid-related diseases, and pharmacology (steroid hormones, membrane-targeting drugs).

  • Quick recap of key atoms and groups to memorize

    • Nonpolar functional group:

    • Methyl (g)

    • Ionic-capable groups (at physiological pH):

    • Carboxyl (c), Amino (d), Sulfhydryl (e), Phosphate (f)

    • Functional groups and their typical roles:

    • Hydroxyl (a) – alcohols, polarity

    • Carbonyl (b) – ketones/aldehydes (context-dependent)

    • Carboxyl (c) – acids, fatty acids

    • Amino (d) – bases/charge at physiological pH

    • Sulfhydryl (e) – thiols, possible ionization

    • Phosphate (f) – phosphate esters, buffering capacity

    • Methyl (g) – nonpolar tail