A carboxylic acid treated with sufficient strong base can lose both its acidic O–H proton and an alpha C–H proton. Carbon alkylation of the resulting dianion followed by protonation yields an alpha-substituted acid.

Reaction of an enolate with an acyl electrophile. carbon acylation of a ketone enolate gives a 1,3-diketone; O-acylation gives a different connectivity.

Preference for forming or reacting one enolate of a carbonyl compound with more than one alpha site. A less substituted kinetic enolate and an equilibrated more substituted enolate can give different carbon skeletons.

An enolate preferentially formed under conditions where deprotonation site selection is not equilibrated, often at a less hindered alpha carbon with a bulky strong base.

An enolate favoured after equilibration under the stated conditions. It is often more substituted, but aggregation, solvent and counterion can change the preference.

An enolate derived by deprotonation alpha to an ester carbonyl.

An enolate whose nucleophilic carbon is conjugated to a carbonyl through an additional unsaturated unit.

The pectoral girdle supports the anterior paired appendages and connects them with the trunk. In humans, the scapula and clavicle provide a mobile arrangement for the upper limb. Comparative anatomy asks which components and connections are shared among vertebrate lineages.

The pelvic girdle connects the hindlimbs to the axial skeleton through the pelvic bones and their articulations. It transfers loads while enclosing and supporting pelvic structures. Its arrangement differs among vertebrates according to posture, locomotion and reproductive constraints.

An anatomical joint is a connection between skeletal elements. Connections can allow extensive movement, as in a synovial joint, or provide a more restricted union. The category concerns the connection itself and does not require a fluid-filled cavity in every case.

Ordinary vesicle budding and fusion preserve which side of a membrane a protein domain faces: a cytoplasmic domain remains cytoplasmic, and a luminal domain remains luminal. Invagination can enclose previously external space without transporting its contents through a bilayer. The endoplasmic reticulum lumen is continuous with the space between the two nuclear envelope membranes; it is not the chromosome-containing nucleoplasm. Any proposed evolutionary remodelling must account for these distinct spaces and the membrane connections between them.

The E blastomere produces the intestinal lineage. Maternal SKN-1 and the P2-to-EMS inductive interaction converge on an endoderm gene regulatory network with parallel inputs and partly redundant GATA transcription factors. Loss of one late marker does not establish loss of the lineage.^[ref]

The embryonic endoderm population specified during gastrulation, distinguished from earlier extraembryonic primitive endoderm. In mouse, resulting gut endoderm can include intercalated cells from distinct histories.

An iminium intermediate can lose a proton at either adjacent carbon, generating different enamine double-bond positions. Reaction selectivity can depend on which regioisomer is populated.

A porous gel changes the electrophoretic mobility of charged synthetic polymers through confinement, deformation and pore-to-pore dynamics. Free-draining charge and friction can both grow proportionally to chain length, leaving free-solution mobility nearly length independent; matrix obstruction adds size sensitivity. reptation supplies one weak-field long-chain regime, not a universal calibration. Matrix concentration, effective charge, solvent conditions, conformation, topology, adsorption, electro-osmotic drift and heating can all alter migration. Size standards should match the relevant chemistry and operating regime.

Electronic excitation occurs rapidly compared with nuclear motion. In the Condon approximation, vibronic intensities are proportional to squared overlaps of initial and final vibrational wavefunctions; vertical arrows on a potential diagram summarize this overlap rather than a nuclear trajectory.

A sequence of vibronic transitions sharing a lower vibrational level and reaching successive vibrational levels of another electronic state. frequency differences remove the common electronic origin and reveal vibrational spacings.

A two-index arrangement of vibronic transition wavenumbers. Differences along rows isolate lower-state spacings; differences down columns isolate upper-state spacings. Deviations from exact separability can expose measurement uncertainty, rotational structure or incorrect assignments.

A scale proportional to the average spectroscopic one-electron binding energy of a free ground-state atom’s valence electrons. For an s,p atom, $\chi =C(n_s{\epsilon }_s+n_p{\epsilon }_p)/(n_s+n_p)$, with positive binding energies and a scale constant $C$. It distinguishes s and p binding rather than assigning both one Slater charge.^[ref]